INTRODUCTION

Waterproofing of surfaces above grade is the prevention of water intrusion into exposed elements of a structure or its components. Above-grade materials are not subject to hydrostatic pressure but are exposed to detrimental weathering effects such as ultraviolet light.

Water that penetrates above-grade envelopes does so in five distinct methods:
● Natural gravity forces
● Capillary action
● Surface tension
● Air pressure differential
● Wind loads

The force of water entering by gravity is greatest on horizontal or slightly inclined enve- lope portions. Those areas subject to ponding or standing water must be adequately sloped to provide drainage away from envelope surfaces.

Capillary action is the natural upward wicking motion that can draw water from ground sources up into above-grade envelope areas. Likewise, walls resting on exposed horizontal portions of an envelope (e.g., balcony decks) can be affected by capillary action of any ponding or standing water on these decks.

The molecular surface tension of water allows it to adhere to and travel along the under- side of envelope portions such as joints. This water can be drawn into the building by gravity or unequal air pressures.

If air pressures are lower inside a structure than on exterior areas, water can be literally sucked into a building. Wind loading during heavy rainstorms can force water into interi- or areas if an envelope is not structurally resistant to this loading. For example, curtain walls and glass can actually bend and flex away from gaskets and sealant joints, causing direct access for water.

The above-grade envelope must be resistant to all these natural water forces to be water- tight. Waterproofing the building envelope can be accomplished by the facade material itself (brick, glass, curtain wall) or by applying waterproof materials to these substrates. Channeling water that passes through substrates back out to the exterior using flashing, weeps, and damp-proofing is another method. Most envelopes include combinations of all these methods.

Older construction techniques often included masonry construction with exterior load bearing walls up to 3-ft thick. This type of envelope required virtually no attention to waterproofing or weathering due to the shear impregnability of the masonry wall.

Today, however, it is not uncommon for high-rise structures to have an envelope skin thickness of  1 8 in. Such newer construction techniques have developed from the need for lighter-weight systems to allow for simpler structural requirements and lower building costs.

These systems, in turn, create problems in maintaining an effective weatherproof envelope.
Waterproof building surfaces are required at vertical portions as well as horizontal applications such as balconies and pedestrian plaza areas. Roofing is only a part of necessary above-grade waterproofing systems, one that must be carefully tied into other building envelope components.

Today roofing systems take many different forms of design and detailing. Plaza decks or balcony areas covering enclosed spaces and parking garage floors covering an occupied space all constitute individual parts of a total roofing system. Buildings can have exposed roofs as well as unexposed membranes acting as roofing and waterproofing systems for preventing water infiltration into occupied areas.

Most above-grade materials are breathable in that they allow for negative vapor transmission.
This is similar to human skin; it is waterproof, allowing you to swim and bathe but also to perspire, which is negative moisture transmission. Most below-grade materials will not allow negative transmission and, if present, it will cause the material to blister or become unbonded.

Breathable coatings are necessary on all above-grade wall surfaces to allow moisture condensation from interior surfaces to pass through wall structures to the exterior. The sun causes this natural effect by drawing vapors to the exterior. Pressure differentials that might exist between exterior and interior areas create this same condition.

Vapor barrier (nonbreathable) products installed above grade cause spalling during freeze–thaw cycles. Vapor pressure buildup behind a nonbreathable coating will also cause the coating to disbond from substrates. This effect is similar to window or glass areas that are vapor barriers and cause formation of condensation on one side that cannot pass to exterior areas.

Similarly, condensation passes through porous wall areas back out to the exterior when a breathable coating is used, but condenses on the back of nonbreathable coatings. This buildup of moisture, if not allowed to escape, will deteriorate structural reinforcing steel and other internal wall components.

Below-grade products are neither ultraviolet-resistant nor capable of withstanding thermal movement experienced in above-grade structures. Whereas below-grade materials are not subject to wear, above-grade materials can be exposed to wear such as foot traffic.

Below-grade products withstand hydrostatic pressure, whereas above-grade materials do not. Waterproofing systems properties are summarized in Table 3.1.


Since many waterproofing materials are not aesthetically acceptable to architects or engineers, some trade-off of complete watertightness versus aesthetics is used or specified. For instance, masonry structures using common face brick are not completely waterproof due to water infiltration at mortar joints. Rather than change the aesthetics of brick by applying a waterproof coating, the designer chooses a dampproofing and flashing system. This damp-proofing system diverts water that enters through the brick wall back out to the exterior.

Application of a clear water repellent will also reduce water penetration through the brick and mortar joints. Such sealers also protect brick from freeze–thaw and other weathering cycles.

Thus, waterproofing exposed vertical and horizontal building components can include a combination of installations and methods that together compose a building envelope. This is especially true of buildings that use a variety of composite finishes for exterior surfacing such as brick, precast, and curtain wall systems. With such designs, a combination of several waterproofing methods must be used. Although each might act independently, as a whole they must act cohesively to prevent water from entering a structure. Sealants, wall flashings, weeps, dampproofing, wall coatings, deck coatings, and the natural weathertightness of architectural finishes themselves must act together to prevent water intrusion (Fig. 3.1).

This chapter will cover vertical waterproofing materials, including clear water repellents, elastomeric coatings, cementitious coatings, and related patching materials. It will also review horizontal waterproofing materials including deck coatings, sandwich slab membranes, and roofing.

FIGURE 3.1 All envelope waterproofing applications must act together to prevent water intrusion.

Several systems are available for weatherproofing vertical wall envelope applications. Clear sealers are useful when substrate aesthetics are important. These sealers are typically applied over precast architectural concrete, exposed aggregate, natural stone, brick, or masonry.

It is important to note that clear sealers are not completely waterproof; they merely slow down the rate of water absorption into a substrate, in some situations as much as 98 percent.

However, wind-driven rain and excessive amounts of water will cause eventual leakage through any clear sealer system. This requires flashings, dampproofing, sealants, and other systems to be used in conjunction with sealers, to ensure drainage of water entering through primary envelope barriers.

This situation is similar to wearing a canvas-type raincoat. During light rain, water runs off; but should the canvas become saturated, water passes directly through the coat. Clear sealers as such are defined as water repellents, in that they shed water flow but are not impervious to water saturation or a head of water pressure.

Elastomeric coatings are high-solid-content paints that produce high-millage coatings when applied to substrates. These coatings are waterproof within normal limitations of movement and proper application.

Elastomeric coatings completely cover and eliminate any natural substrate aesthetics. They can, however, add a texture of their own to an envelope system, depending on the amount of sand, if any, in the coating.

To waterproof adequately with an elastomeric coating, details must be addressed, including patching cracks or spalls in substrates, allowing for thermal movement, and installation of flashings where necessary.

Cementitious coatings are available for application to vertical masonry substrates, which also cover substrates completely. The major limitation of cementitious above-grade product use is similar to its below-grade limitation. The products do not allow for any substrate movement or they will crack and allow water infiltration. Therefore, proper attention to details is imperative when using cementitious materials. Installing sealant joints for movement and crack preparation must be completed before cementitious coating application.

With all vertical applications, there are patching materials used to ensure water tightness of the coating applied. These products range from brushable-grade sealants for small cracks, to high-strength, quick-set cementitious patching compounds for repairing spalled substrate areas.

Several types of systems and products are available for horizontal above-grade applications, such as parking garages and plaza decks. Surface coatings, which apply directly to exposed surfaces of horizontal substrates, are available in clear siloxane types or solid coatings of urethane or epoxy. Clear horizontal sealers, as with vertical applications, do not change existing substrate aesthetics to which they are applied. They are, however, not in themselves completely waterproof but only water-resistant.

Clear coatings are often specified for applications, to prevent chloride ion penetration into concrete substrates from such materials as road salts. These pollutants attack rein- forcing steel in concrete substrates and cause spalling and structural deterioration.

Urethane, epoxy, or acrylic coatings change the aesthetics of a substrate but have elastomeric properties that allow bridging of minor cracking or substrate movement. Typically, these coatings have a “wearing coat” that contains silicon sand or carbide, which allows vehicle or foot traffic while protecting the waterproof base coat.

Subjecting coatings to foot or vehicular wear requires maintenance at regular frequency and completion of necessary repairs. The frequency and repairs are dependent on the  type and quantity of traffic occurring over the envelope coating.

As with vertical materials, attention to detailing is necessary to ensure watertightness.

Expansion or control joints must be properly sealed, cracks or spalls in the concrete must be repaired before application, and allowances for drainage must be created.

Several types of waterproof membranes are available for covered decks such as sand- wich slab construction or tile-topped decks. These membranes are similar to those used in below-grade applications, including liquid-applied and sheet-good membranes. Such applications are also used as modified roofing systems.

All above-grade waterproof systems are vulnerable to a host of detrimental conditions due to their exposure to weathering elements and substrate performance under these conditions. Exposure of the entire above-grade building envelope requires resistance from many severe effects, including the following:

● Ultraviolet weathering
● Wind loading
● Structural loading due to snow or water
● Freeze–thaw cycles
● Thermal movement
● Differential movement
● Mildew and algae attack
● Chemical and pollution attack from chloride ions, sulfates, nitrates, and carbon dioxide Chemical and pollution attack is becoming ever more frequent and difficult to contend with. Chloride ions (salts) are extremely corrosive to the reinforcing steel present in all structures, whether it is structural steel, reinforcing steel, or building components such as shelf angles.

Even if steel is protected by encasement in concrete or is covered with a brick facade, water that penetrates these substrates carries chloride ions that attack the steel. Once steel begins to corrode it increases greatly in size, causing spalling of adjacent materials and structural cracking of substrates.

All geographic areas are subject to chloride ion exposure. In coastal areas, salt spray is concentrated and spread by wind conditions; in northern climates, road salts are used during winter months. Both increase chloride quantities available for corrosive effects on envelope components.

Acid rain now affects all regions of the world. When sulfates and nitrates present in the atmosphere are mixed with water, they create sulfuric and nitric acids (acid rain), which affect all building envelope components. Acids attack the calcium compounds of concrete and masonry surfaces, causing substrate deterioration. They also affect exposed metals on a structure such as flashing, shelf angles, and lintel beams.

Within masonry or concrete substrates, a process of destructive weathering called car- bonation occurs to unprotected, unwaterproofed surfaces. Carbonation is the deterioration of cementitious compounds found in masonry substrates when exposed to the atmospheric pollutant carbon dioxide (automobile exhaust).

Carbon dioxide mixes with water to form carbonic acid, which then penetrates a masonry or concrete substrate. This acid begins deteriorating cementitious compounds that form part of a substrate.

Carbonic acid also causes corrosion of embedded reinforcing steel such as shelf angles by changing the substrate alkalinity that surrounds this steel. Reinforcing steel, which is normally protected by the high alkalinity of concrete, begins to corrode when carbonic acid change lowers alkalinity while also deteriorating the cementitious materials.

Roofing systems will deteriorate because of algae attack. Waterproof coatings become brittle and fail due to ultraviolet weathering. Thermal movement will split or cause cracks in a building envelope. This requires that any waterproof material or component of the building envelope be resistant to all these elements, thus ensuring their effectiveness and, in turn, protecting a building during its life-cycling.

Finally, an envelope is also subject to building movement, both during and after construction. Building envelope components must withstand this movement; otherwise, designs must include allowances for movement or cracking within the waterproofing material.

Cracking of waterproofing systems occur because of structural settlement, structuralloading, vibration, shrinkage of materials, thermal movement, and differential movement.

To ensure successful life-cycling of a building envelope, allowances for movement must be made, including expansion and control joints, or materials must be chosen that can withstand expected movement.

All these exposure problems must be considered when choosing a system for water- proofing above-grade envelope portions. Above-grade waterproofing systems include the following horizontal and vertical applications:

● Vertical
● Clear repellents
● Cementitious coatings
● Elastomeric coatings
● Horizontal
● Deck coatings
● Clear deck sealers
● Protected membranes

Although clear sealers do not fit the definition of true waterproofing systems, they do add water repellency to substrates where solid coatings as an architectural finish are not acceptable (see Fig. 3.2.). Clear sealers are applied on masonry or concrete finishes when a repellent that does not change substrate aesthetics is required. Clear sealers are also specified for use on natural stone substrates such as limestone. Water repellents prevent chloride ion penetration into a substrate and prevent damage from the freeze–thaw cycles.

FIGURE 3.2 Repellency of sealer application.

There is some disagreement over the use of sealers in historic restoration. Some prefer stone and masonry envelope components to be left natural, repelling or absorbing water and aging naturally. This is more practical in older structures that have massive exterior wall substrates than in modern buildings. Today exterior envelopes are as thin as  1 8 inch, requiring additional protection such as clear sealers.

The problem with clear sealers is not in deciding when they are necessary but in choosing a proper material for specific conditions. Clear repellents are available in a multitude of compositions, including penetrates and film-forming materials. They vary in percentage of solids content and are available in tint or stain bases to add uniformity to the substrate color.

The multitude of materials available requires careful consideration of all available products to select the material appropriate for a particular situation. Repellents are available in the compositions and combinations shown in Table 3.2. Sealers are further classified into penetrating and film-forming sealers.


Clear sealers will not bridge cracks in the substrate, and this presents a major disadvantage in using these materials as envelope components. Should cracks be properly pre- pared in a substrate before application, effective water repellency is achievable. However, should further cracking occur, due to continued movement, a substrate will lose its watertightness. Properly designed and installed crack-control procedures, such as control joints and expansion joints, alleviate cracking problems.

Figure 3.3 shows a precast cladding after rainfall with no sealer applied. Water infil- trating the precast can enter the envelope and bypass sealant joints into interior areas.

Figure 3.4 demonstrates just how effective sealers can be in repelling water.

FIGURE 3.3 Precast concrete building with no sealer permits water absorption.

FIGURE 3.4 Effectiveness of sealer application is evident after a rainfall.

 Film-forming sealers

Film-forming, or surface, sealers have a viscosity sufficient to remain primarily on top of a substrate surface. Penetrating sealers have sufficiently low viscosity of the vehicle (binder and solvent) to penetrate into masonry substrate pores. The resin molecule sizes of a sealer determine the average depth of penetration into a substrate.

Effectiveness of film-forming and penetrating sealers is based upon the percentage of solids in the material. High-solid acrylics will form better films on substrates by filling open pores and fissures and repelling a greater percentage of water. Higher-solids-content materials are necessary when used with very porous substrates; however, these materials may darken or impart a glossy, high sheen appearance to a substrate.

Painting or staining over penetrating sealers is not recommended, as it defeats the purpose of the material. With film-forming materials, if more than a stain is required, it may be desirable to use an elastomeric coating to achieve the desired watertightness and color.

Most film-forming materials and penetrates are available in semitransparent or opaque formulations. If it is desired to add color or a uniform coloring to a substrate that may contain color irregularities (such as tilt-up or poured-in-placed concrete), these sealers offer effective solutions. (See Table 3.3)


Penetrating sealers

Penetrating sealers are used on absorptive substrates such as masonry block, brick, concrete, and porous stone. Some penetrating sealers are manufactured to react chemically with these substrates, forming a chemical bond that repels water. Penetrating sealers are not used over substrates such as wood, glazed terra cotta, previously painted surfaces, and exposed aggregate finishes.

On these substrates, film-forming clear sealers are recommended (which are also used on masonry and concrete substrates). These materials form a film on the surface that acts as a water-repellent barrier. This makes a film material more susceptible to erosion due to ultraviolet weathering and abrasive wear such as foot traffic.

Penetrating sealers are breathable coatings, in that they allow water vapor trapped in a substrate to escape through the coating to the exterior. Film-forming sealers’ vapor trans- mission (perm rating) characteristics are dependent on their solids content. Vapor trans- mission or perm ratings are available from manufacturers. Permeability is an especiallyimportant characteristic for masonry installed at grade line. Should an impermeable coating be applied here, moisture absorbed into masonry by capillary action from ground sources will damage the substrates, including surface spalling.

Many sealers fail due to a lack of resistance to alkaline conditions found in concrete and masonry building materials. Most building substrates are high in alkalinity, which causes a high degree of failure with poor alkaline-resistant sealers.

Penetrating materials usually have lower coverage rates and higher per-gallon costs than film materials. Penetrating sealers, however, require only a one-coat application versus two for film-forming materials, reducing labor costs.

Penetrating and film-forming materials are recognized as effective means of preventing substrate deterioration due to acid rain effects. They prevent deterioration from air and water pollutants and from dirt and other contaminants by not allowing these pollutants to be absorbed into a substrate. (See Table 3.4.)

Without any doubt, choosing the correct water repellent for a specific installation can be a difficult task.
Sealer manufacturers offer you little assistance as you try to find your way through the maze of products available, reported to be as many as 500 individual systems.

Even though there is a finite number of families of sealers, as outlined in the following sections, within each family manufacturers will try to differentiate themselves from all others, even though most are very similar systems.

There are numerous chemical formulations created using the basic silicon molecule that forms the basis for most of the penetrating sealers. These formulations result in the basic family groups of: Silicones, Silicates, Silanes, and Siloxanes. There is often confusion as to the basic families of sealers; for example, some will classify Siliconates as a family even though it begins as a derivative of a Silane. From these basic groups, manufacturers formulate numerous minor changes that offer little if any improvements and only tend to con- fuse the purchaser into thinking they are buying something totally unique.

Derivatives include Alkylalkoxysiloxane (siloxane), Isobutyltrialkoxysilane (silane), Alkylalkoxysilane (silane), methylsiloxanes, and many blends of the family groups such as a silane/siloxane combination. These formulations or chemical combinations should not confuse a prospective purchaser. With a few basic guidelines, the best selection for each individual installation can be made easily.

First, any water repellent used should have the basic characteristics necessary for all types of installations: sufficient water repellency, and long life-cycling under alkaline conditions. The latter, performance in alkaline conditions, usually controls how well the product will perform as a repellent over extended life cycling. For the penetrating sealers listed above, no matter how well the product repels water during laboratory testing, the product will virtually become useless after installation if it cannot withstand the normal alkaline conditions of concrete or masonry substrates. Concrete in particular has very high alkaline conditions that can alter the chemical stability of penetrating sealers, resulting in a complete loss of repellency capability.

Therefore when reviewing manufacturer’s guide specifications, the high initial repellency rates should not be depended upon solely; rather emphasize the test results of accelerated weathering, especially when application is used on concrete or precast concrete substrates. Verify that the accelerated weathering is tested on a similar substrate, as masonry or most natural stones will not have alkaline conditions as high as concrete.

In addition, when the proposed application is over concrete substrates with substantial reinforcing steel embedded, the resistance of the repellent to chloride ion infiltration should be highlighted. Chlorides attack the reinforcing steel and can cause structural dam- age after extended weathering. Many sealers have very poor chloride resistance.

Since water penetration begins on the surface, depth of penetration is not a particularly important consideration. While all penetrating sealers must penetrate sufficiently to react chemically with the substrate, many penetration depth claims are made on the solvent carrier rather than the chemical solids that form the repellency. The effective repellency must be at the surface of the substrate to repel water. Water should only penetrate the surface if there is cracking in the substrate, and if this is the case, no repellent can bridge cracking or penetrate sufficiently to repel water in the crack crevice (see Fig. 3.5).

FIGURE 3.5 Clear repellents cannot repel water entering through substrate cracks.

Penetrating capability is a better guide for a sealer’s protection against UV degradation.

Having the active compounds deeper into the substrate surface protects the molecules from the sun’s ultraviolet rays that can destroy a sealers repellency capability.

When comparing the capability of sealers to penetrate into a substrate be sure to review what is referred to as the uniform gradient permeation (UPG), which measures the penetration of the active ingredient rather than the solvent carrier. Most alcohol carriers will penetrate with the active ingredient deeper than those using a petroleum-based carrier will.

Some manufacturers will make claims as to the size of their active molecules being so small that they penetrate better than other compounds using larger molecules. While this may be the case, compounds with larger molecules usually repel water better than those using smaller molecules.

The amount of solids or active ingredient is always a much-trumpeted point of comparison. Certainly, there is a minimum amount of solids or active agent to produce the required repellency, but once this amount is exceeded there is no logic as to what a greater concen- tration will do. For the majority of penetrating sealers, 10 percent active compounds seems to be the minimum to provide sufficient water repellency, with 20 percent moving towards the maximum return for the amount of active agent necessary. While manufacturers will often exceed this to increase a product’s sales potential, the value of its in-place service capability is often no more than those with a smaller percentage of active compounds.

When considering film-forming repellents, a greater percentage of solids is important since these solids are deposited directly on the surface of the substrate and left to repel water directly and without the assistance of the substrate environment. With film-forming repellents, the closer to 100 percent solids, the more likely the repellent will be capable of repelling water.

When trying to compare products through the maze of contradictory and confusing information available, it is best to review the results of completed standard and uniform tests that are most appropriate for the substrate and service requirements required. The next section expands on the most frequently used testing to compare products, a much better guide than reading sales literature about percent solids, size of molecule, and chemical formulations. In most cases it is not appropriate to make comparison without the use of standard testing, and no product should be considered without this critical information being provided. Recognize however, that these tests are conducted in the pristine conditions of a laboratory that are never duplicated under actual field conditions. This requires that a sufficient margin of error or safety factor be used for actual expectations of performance results in actual installations.

Sealer testing

Several specific tests should be considered in choosing clear sealers. Testing most often referred to is the National Cooperative Highway Research Program (NCHRP). This is the most appropriate test for concrete substrates including bridges and other civil construction projects. Although often used for testing horizontal applications, it remains an effective test for vertical sealers as well. NCHRP test 244, Series II, measures the weight gain of a substrate by measuring water absorption into a test cube submerged after treatment with  a selected water repellent. To be useful, a sealer should limit weight gain to less than 15 percent of original weight and preferably less than 10 percent. Test results are also referred to as “a reduction in water absorption from the control [untreated] cube.” These limits should be an 85–100 percent reduction, preferably above 90 percent.

Testing by ASTM includes ASTM D-514,Water Permeability of Masonry, ASTM C-67, Water Repellents Test, and ASTM C-642, Water Absorption Test. Also, federal testing by test SS-W-110C includes water absorption testing.

Any material chosen for use as a clear sealer should be tested by one of these methods to determine water absorption or repellency. Effective water repellency should be above 85 percent, and water absorption should be less than 20 percent, preferably 15–10 percent.

Weathering characteristics are important measures of any repellent, due to the alkaline conditions of most masonry and concrete substrates that will deter or destroy the water repellency capabilities of penetrating sealers. In addition, UV degradation affects the life-cycle repellency capabilities for both film-forming and penetrating sealers. Accelerated weathering testing, ASTM 793-75, is an appropriate test to determine the capabilities of a sealer to perform over an extended period. Be sure that the testing is used on a similar substrate, however, as the alkaline conditions of concrete are more severe that masonry products.

Of course, it is always appropriate to test for the compatibility of the sealer with other envelope components and on the exact substrate on which it will be applied. This testing will ensure that there will be no staining of the substrate, that the sealer can penetrate sufficiently, and that the sealer does not damage adjacent envelope components such as glass or aluminum curtain wall etching and sealants, as well as surrounding landscaping.

Acrylics

Acrylics and their derivatives, including methyl methacrylates, are film-forming repellents.
Acrylics are formulated from copolymers of acrylic or methocrylic acids. Their penetration into substrates is minimal, and they are therefore considered film-forming sealers. Acrylic derivatives differ by manufacturer, each having its own proprietary formulations.

Acrylics are available in both water- and solvent-based derivatives. They are frequently used when penetrating sealers are not acceptable for substrates such as exposed aggregate panels, wood, and dense tile. They are also specified for extremely porous surfaces where a film buildup is desirable for water repellency.

Acrylics do not react chemically with a substrate, and form a barrier by filming over surfaces as does paint. Solids content of acrylics varies from 5 to 48 percent. The higher a solid’s content, the greater the amount of sheen imparted to a substrate. High-solids materials are sometimes used or specified to add a high gloss or glazed appearance to cementitious finish materials such as plaster. Methyl methacrylates are available in 5–25 percent solids content.

Most manufacturers require two-coat applications of acrylic materials for proper coverage and uniformity. Coverage rates vary depending on the substrate and its porosity, with first coats applied at 100–250 ft^2/gal. Second coats are applied 150–350 ft^2/gal. Acrylics should not be applied over wet substrates, as solvent-based materials may turn white if applied under these conditions. They also cannot be applied in freezing temperatures or over a frozen substrate.

Higher-solids-content acrylics have the capability of being applied in sufficient millage to fill minor cracks or fissures in a substrate. However, no acrylic is capable of withstanding movement from thermal or structural conditions. Acrylic sealers have excellent adhesion when applied to properly prepared and cleaned substrates. Their application resists the formation of mildew, dirt buildup, and salt and atmospheric pollutants.

Acrylics are available in transparent and opaque stains. This coloring enables hiding or blending of repairs to substrates with compatible products such as acrylic sealants and patching compounds. Stain products maintain existing substrate textures and do not oxi- dize or peel as paint might.

Acrylics are compatible with all masonry substrates including limestone, wood, aggregate panels, and stucco that has not previously been sealed or painted. Acrylic sealers are not effective on very porous surfaces such as lightweight concrete block. The surface of this block contains thousands of tiny gaps or holes filled with trapped air. The acrylic coatings cannot displace this trapped air and are ineffective sealers over such substrates. (See Table 3.5.)



Silicones

Silicone-based water repellents are manufactured by mixing silicone solids (resins) into a solvent carrier. Most manufacturers base their formulations on a 5 percent solids mixture, in conformance with the requirements of federal specification SS-W-110C.

Although most silicone water repellents are advertised as penetrating, they function as film-forming sealers. Being a solvent base allows the solid resin silicone to penetrate the surface of a substrate, but not to depths that siloxanes or quartz carbide sealers penetrate.

The silicone solids are deposited onto the capillary pores of a substrate, effectively forming a film of solids that repels water.

All silicone water repellents are produced from the same basic raw material, silane.
Manufacturers are able to produce a wide range of repellents by combining or reacting different compounds with this base silane material. These combinations result in a host of silicone-based repellents, including generic types of siliconates, silicone resins, silicones, and siloxanes. The major difference in each of these derivatives is its molecular size.

Regardless of derivative type, molecular size, or compound structure, all silicone-based repellents repel water in the same way. By penetrating substrates, they react chemically with atmospheric moisture, by evaporation of solvents, or by reaction with atmospheric carbon dioxide to form silicone resins that repel water.

Only molecular sizes of the final silicone resin are different. Silicone-based products require that silica be present in a substrate for the proper chemical actions to take place.

Therefore, these products do not work on substrates such as wood, metal, or natural stone.
A major disadvantage of silicone water repellents is their poor weathering resistance.
Ultraviolet-intense climates can quickly deteriorate these materials and cause a loss of their water repellency. Silicone repellents are not designed for horizontal applications, as they do not resist abrasive wearing.

Silicone repellents are inappropriate for marble or limestone substrates, which discolor if these sealer materials are applied. Discoloring can also occur on other substrates such as precast concrete panels. Therefore, any substrate should be checked for staining by a test application with the proposed silicone repellent.

Lower-solid-concentration materials of 1–3 percent solids are available to treat substrates subject to staining with silicone. These formulations should be used on dense surface materials such as granite to allow proper silicone penetration. Special mixes are manufactured for use on limestone but also should be tested before actual application. Silicones can yellow after application, aging, or weathering.

As with most sealers, substrates will turn white or discolor if applied during wet conditions. Silicones do not have the capabilities to span or bridge cracking in a substrate.

Very porous materials, such as lightweight or split-face concrete blocks, are not acceptable substrates for silicone sealer application. Adjacent surfaces such as windows and vegetation should be protected from overspray during application. (See Table 3.6.)


Urethanes

Urethane repellents, aliphatic or aromatic, are derivatives of carbonic acid, a colorless crystalline compound. Clear urethane sealers are typically used for horizontal applications but are also used on vertical surfaces. With a high solids content averaging 40 percent, they have some ability to fill and span nonmoving cracks and fissures up to  1 16 in wide. High-solids materials such as urethane sealers have low perm ratings and cause coating blistering if any moisture or vapor drive occurs in the substrate.

Urethane sealers are film-forming materials that impart a high gloss to substrates, and they are nonyellowing materials. They are applicable to most substrates including wood and metal, but adhesive tests should be made before each application. Concrete curing agents can create adhesion failures if the surface is not prepared by sandblasting or acid etching.

Urethane sealers can also be applied over other compatible coatings, such as ure- thane paints, for additional weather protection. They are resistant to many chemicals, acids, and solvents and are used on stadium structures for both horizontal and vertical seating sections. The cost of urethane materials has limited their use as sealers. (SeeTable 3.7.)


Silanes

Silanes contain the smallest molecular structures of all silicone-based materials. The small molecular structure of the silane allows the deepest penetration into substrates. Silanes, like siloxanes, must have silica present in substrates for the chemical action to take place that provides water repellency. These materials cannot be used on substrates such as wood, metal, or limestone that have no silica present for chemical reaction.

Of all the silicone-based materials, silanes require the most difficult application procedures. Substrates must have sufficient alkalinity in addition to the presence of moisture to produce the required chemical reaction to form silicone resins. Silanes have high volatility that causes much of the silane material to evaporate before the chemical reaction forms the silicon resins. This evaporation causes a high silane concentration, as much as 40 percent, to be lost through evaporation.

Should a substrate become wet too quickly after application, the silane is washed out from the substrate-prohibiting proper water-repellency capabilities. If used during extremely dry weather, after application substrates are wetted to promote the chemical reaction necessary. The wetting must be done before all the silane evaporates.

As with other silicone-based products, silanes applied properly form a chemical bond with a substrate. Silanes have a high repellency rating when tested in accordance with

ASTM C-67, with some products achieving repellency over 99 percent. As with urethane sealers, their high cost limits their usage. (See Table 3.8.)



Siloxanes

Siloxanes are produced from the CL-silane material, as are other silicone masonry water repellents. Siloxanes are used more frequently than other clear silicones, especially for horizontal applications. Siloxanes are manufactured in two types, oligomerous (short chain of molecular structure) and polymeric (longer chain of molecular structure) alky-lalkoxysiloxanes.

Most siloxanes produced now are oligomerous. Polymeric products tend to remain wet or tacky on the surface, attracting dirt and pollutants. Also, polymeric siloxanes have poor alkali resistance, and alkalis are common in masonry products for which they are intended.

Oligomerous siloxanes are highly resistant to alkaline attack, and therefore can be used
 successfully on high alkaline substrates such as cement-rich mortar.

Siloxanes react with moisture, as do silanes, to form the silicone resin that acts as the water-repellent substance. Upon penetration of a siloxane into a substrate it forms a chemical bond with the substrate. The advantage of siloxanes over silanes is that their chemical structure does not promote a high evaporation rate.

The percentage of siloxane solids used is substantially less (usually less than 10 percent for vertical applications), thereby reducing costs. Chemical reaction time is achieved faster with siloxanes, which eliminates a need for wetting after installation. Repellency is usually achieved within 5 hours with a siloxane.

Siloxane formulations are now available that form silicone resins without the catalyst— alkalinity—required. Chemical reactions with siloxanes take place even with a neutral sub- strate as long as moisture, in the form of humidity, is present.

These materials are suitable for application to damp masonry surfaces without the masonry turning white, which might occur with other materials. Testing of all substrates should be completed before full application, to ensure compatibility and effectiveness of the sealer.

Siloxanes do not change the porosity or permeability characteristics of a substrate. This allows moisture to escape without damaging building materials or the repellent. Since siloxanes are not subject to high evaporation rates, they can be applied successfully by high-pressure sprays for increased labor productivity.

Siloxanes, as other silicone-based products, may not be used with certain natural stones such as limestone. They also are not applicable to gypsum products or plaster. Siloxanes should not be applied over painted surfaces, and if surfaces are to be painted after treatment they should first be tested for compatibility. (See Table 3.9.)


Silicone rubber

These systems are a hybrid of the basic silicone film-forming and the silicone derivatives penetrating sealers. The product is basically a silicone solid dissolved in a solvent carrier that penetrates into the substrate, carrying the solids to form a solid film that is integral with the substrate. Unlike the penetrating derivatives, silicone rubbers do not react with the substrate to form the repellency capability.

The percentage solids, as high as 100 percent, carried into the substrate supposedly create a thickness of product millage internally in the substrate to a film thick enough to bridge minute hairline cracking in the substrate. This elongation factor, expressed as high as 400 percent by some manufacturers, does not produce substantial capacity to bridge cracks, since the millage of the film that creates movement capability is minimal with clear repellents. Only existing cracks less than 1/ 32 in are within the capability of these materials to seal, and new cracks that develop will not be bridged since the material is integral with the substrate and cannot move as film-forming membranes are allowed to do.

Through chemical formulations and the fact that they penetrate into the substrate, the silicone rubber products have been UV-retardant, unlike basic silicone film-forming sealers. At the same time they retain sufficient permeability ratings to permit applications to typical clear repellent substrates. These systems are also applicable to wood, canvas, and terra cotta substrates that other penetrating sealers are not applicable, since the rubber systems do not have to react with the substrate to form their repellency.

Silicone rubber systems are applicable in both horizontal and vertical installations and make excellent sealers for civil project sealing including bridges, overpasses, and parking garages. Like the generic silicone compounds, silicone rubber does not permit any other material to bond to it directly. Therefore, projects sealed with these materials can not be painted over in the future without having to remove the sealer with caustic chemicals such as solvent paint removers. This can create problems on projects where some applications are required over the substrate once sealed, such as parking-stall painted stripes in a parking garage. Manufacturers of the silicone rubber sealers should be contacted directly for  recommendations in such cases.

These materials generally have excellent repellency rates in addition to acceptable permeability rates. Overspray precautions should be taken whenever using the product near glass or aluminum envelope components, since the material is difficult if not almost impossible to remove from such substrates. (See Table 3.10).



Sodium silicates

Sodium silicate materials should not be confused with water repellents. They are concrete densifiers or hardeners. Sodium silicates react with the free salts in concrete such as calcium or free lime, making the concrete surface more dense. Usually these materials are sold as floor hardeners, which when compared to a true, clear deck coating have repellency insufficient to be considered with materials of this section.

General surface preparations for all clear water-repellent applications require that the substrate be clean and dry. (Siloxane applications can be applied to slightly damp surfaces, but it is advisable to try a test application.) All release agents, oil, tar, and asphalt stains, as well as efflorescence, mildew, salt spray, and other surface contaminants, must be removed.

Application over wet substrates will cause either substrate discoloring, usually a white film formation, or water-repellent failure. When in doubt of moisture content in a substrate, do a moisture test using a moisture meter or a mat test using visquene taped to a wall, to check for condensation. Note that some silicone-based systems, such as silanes, must have moisture present, usually in the form of humidity, to complete the chemical reaction.

Substrate cracks are repaired before sealer application. Small cracks are filled with nonshrink grout or a sand–cement mixture. Large cracks or structural cracking should be epoxy-injected. If a crack is expected to continue to move, it should be sawn out to a min- imum width of  1 4 in and sealed with a compatible sealant.

Note that joint sealers should be installed first, as repellents contaminate joints, causing sealant-bonding failure. Concrete surfaces, including large crack patching, should be cured a minimum of 28 days before sealer application.

All adjacent substrates not being treated, including window frames, glass, and shrubberies, should be protected from overspray. Natural stone surfaces, such as limestone, are susceptible to staining by many clear sealers. Special formulations are available from manufacturers for these substrates. If any questions exist regarding an acceptable substrate for application, a test area should first be completed.

All sealers should be used directly from purchased containers. Sealers should never be thinned, diluted, or altered. Most sealers are recommended for application by low-pressure spray (20 lb/in2), using a Hudson or garden-type sprayer. Brushes or rollers are also acceptable, but they reduce coverage rates. High-pressure spraying should be used only if approved by the manufacturer.

Applicators should be required to wear protective clothing and proper respirators, usually the cartridge type. Important cautionary measures should be followed in any occupied structure. Due to the solvents used in most clear sealers, application areas must be well ventilated.

All intake ventilation areas must be protected or shut off, to prevent the contamination of interior areas from sealer fumes. Otherwise, evacuation by building occupants is necessary.

Most manufacturers require a flood coating of material, with coverage rates dependent upon the substrate porosity. Materials should be applied from the bottom of a building, working upward (Fig. 3.6). Sealers are applied to produce a rundown or saturation of about 6 in of material below the application point for sufficient application. If a second coat is required, it should be applied in the same manner. Coverage rates for second coats increase, as fewer materials will be required to saturate a substrate surface.

FIGURE 3.6 Spray application of clear repellent.

Testing should be completed to ensure that saturation of surfaces will not cause darkening or add sheen to substrate finishes. Dense concrete finishes may absorb insufficient repellent if they contain admixtures such as integral waterproofing or form-release agents.

In these situations, acid etching or pressure cleaning is necessary to allow sufficient sealer absorption. Approximate coverage rates of sealers over various substrates are summarized in Table 3.11.

Priming is not required with any type of clear sealer. However, some manufacturers recommend that two saturation coats be applied instead of one coat. Some systems may require a mist coat to break surface tension before application of the saturation coat.

Cementitious-based coatings are among the oldest products used for above-grade water-proofing applications. Their successful use continues today, even with the numerous clear and elastomeric sealers available. However, cementitious systems have several disadvantages, including an inability to bridge cracks that develop in substrates after application.

This can be nullified by installation of control or expansion joints to allow for movement.

In remedial applications where all settlement cracks and shrinkage cracks have already developed, only expansion joints for thermal movement need be addressed.

These coatings are cement-based products containing finely graded siliceous aggregates that are nonmetallic. Pigments are added for color; proprietary chemicals are added for integral waterproofing or water repellency. An integral bonding agent is added to the dry mix, or a separate bonding agent liquid is provided to add to the dry packaged material during mixing. The cementitious composition allows use in both above- and below-grade applications. See Fig. 3.7, for a typical above-grade cementitious application.

FIGURE 3.7 Spray application of cementitious waterproofing.

Since these products are water-resistant, they are highly resistant to freeze–thaw cycles; they eliminate water penetration that might freeze and cause spalling. Cementitious coatings have excellent color retention and become part of the substrate. They are also non- chalking in nature.

Color selections, such as white, that require the used of white Portland cement, increase material cost. Being cementitious, the product requires job-site mixing, which should be carefully monitored to ensure proper in-place performance characteristics of coatings.

Also, different mixing quotients will affect the dried finish coloring, and if each batch is not mixed uniformly, different finish colors will occur.

Cementitious properties
Cementitious coatings have excellent compressive strength, ranging from 4000 to 6000 lb/in2 after curing (when tested according to ASTM C-109). Water absorption rates of cementitious materials are usually slightly higher than elastomeric coatings. Rates are acceptable for water- proofing, and range from 3 to 5 percent maximum water absorption by weight (ASTM C-67).

Cementitious coatings are highly resistant to accelerated weathering, as well as being salt-resistant. However, acid rain (sulfate contamination) will deteriorate cementitious coatings as it does other masonry products.

Cementitious coatings are breathable, allowing transmission of negative water vapor.

This avoids the need for completing drying of substrates before application, and the spalling that is caused by entrapped moisture. These products are suitable for the exterior of planters, undersides of balconies, and walkways, where negative vapor transmission is likely to occur. Cementitious coatings are also widely used on bridges and roads, to protect exposed concrete from road salts, which can damage reinforcing steel by chloride attack.

Cementitious installations
Water entering masonry substrates causes brick to swell, which applies pressure to adjacent mortar joints.

The cycle of swelling when wet, and relaxing when dry, causes mortar joint deterioration. Cementitious coating application prevents water infiltration and the resulting deterioration. However, coatings alter the original facade aesthetics, and a building owner or architect may deem them not acceptable.

Cementitious coatings are only used on masonry or concrete substrates, unlike elas- tomeric coatings that are also used on wood and metal substrates. Cementitious coating use includes applications to poured-in-place concrete, precast concrete, concrete block units, brick, stucco, and cement plaster substrates (Fig. 3.8). Once applied, cementitious coatings bond so well to a substrate that they are considered an integral part of the substrate rather than a film protection such as an elastomeric coating.

FIGURE 3.8 Block cavity wall waterproofing using cementitious waterproofing.

Typical applications besides above-grade walls include swimming pools, tunnels, retention ponds, and planters (Fig. 3.9). With Environmental Protection Agency (EPA) approval, these products may be used in water reservoirs and water treatment plants. Cementitious coatings are often used for finishing concrete, while at the same time providing a uniform substrate coloring.

FIGURE 3.9 Typical detailing of tunnel waterproofing applicable to above-grade applications.

An advantage with brick or block wall applications is that these substrates do not nec- essarily have to be tuck-pointed before cementitious coating application. Cementitious coatings will fill the voids, fissures, and honeycombs of concrete and masonry surfaces, effectively waterproofing a substrate (Fig. 3.10).

FIGURE 3.10 Waterproofing concrete block envelope with cementitious coating

When conditions require, complete coverage of the substrate by a process called bag, or face, grouting of the masonry is used as an alternative. In this process, a cementitious coating is brush applied to the entire masonry wall. At an appropriate time, the cementi-tious coating is removed with brushes or burlap bags, again revealing the brick and mortar joints. The only coating material left is that in the voids and fissures of masonry units and mortar joints. Although costly, this is an extremely effective means of waterproofing a substrate, more effective only than tuck-pointing.

Complete cementitious applications provide a highly impermeable surface and are used to repair masonry walls that have been sandblasted to remove existing coatings and walls that are severely deteriorated. Cementitious applications effectively preserve a facade while making it watertight. Bag grouting application adds only a uniformity to substrate color; colored cementitious products can impart a different color to existing walls if desired. Mask grouting is similar to bag grouting. With mask grouting applications, existing masonry units are carefully taped over, exposing only mortar joints. The coating material is brush-applied to exposed joints, then cured. Tape is then removed from the masonry units, leaving behind a repaired joint surface with no change in wall facade color.

The thickness of coating added to mortar joints is variable but is greater when joints are recessed. This system is applicable only to substrates in which the masonry units themselves, such as brick, are nondeteriorated and watertight, requiring no restoration.

Texture is easily added to a cementitious coating, either by coarseness of aggregate added to the original mix or by application methods. The same cementitious mix applied by roller, brush, spray, hopper gun, sponge, or trowel results in many different texture finishes. This provides an owner or designer with many texture selections while maintaining adequate waterproofing characteristics. A summary of the major advantages and disadvantages of cementitious coatings are given in Table 3.12.

Cementitious Coating Properties

In certain instances, such as floor–wall junctions, it is desirable first to apply the cementitious coating to a substrate, and then to fill the joint with sealant material in a color that matches the cementitious coating. The coating will fully adhere to the substrate and is com-patible with sealant materials. It is also possible first to apply cementitious coating to sub- strates, then to apply a sealant to expansion joints, door, and window penetrations, and other joints. This is not possible with clear sealers nor recommended with elastomeric coatings, due to bonding problems.

Cementitious coatings are a better choice over certain substrates, particularly concrete or masonry, than clear sealers or elastomeric coatings. This is because cementitious coat- ings have better bonding strength, a longer life cycle, lower maintenance, and less attrac- tion of airborne contaminants. Provided that adequate means are incorporated for thermal and structural movement, cementitious coatings will function satisfactorily for above-and below-grade waterproofing applications.

For adequate bonding to substrates, surfaces to receive cementitious coatings should be cleaned of contaminants including dirt, efflorescence, form-release agents, laitance, residues of previous coatings, and salts. Previously painted surfaces must be sandblasted or chemically cleaned to remove all paint film.

Cementitious coating bonding is critical to successful in-place performance. Therefore, extreme care should be taken in preparing substrates for coating application. Sample applications for bond strength should be completed if there is any question regarding the acceptability of a substrate, especially with remedial waterproofing applications.

Poured-in-place or precast concrete surfaces should be free of all honeycombs, voids, and fins. All tie holes should be filled before coating application with nonshrink grout material as recommended by the coating manufacturer. Although concrete does not need to be cured before cementitious coating application, it should be set beyond the green stage of curing. This timing occurs within 24 hours after initial concrete placement.

With smooth concrete finishes, such as precast, surfaces may need to be primed with a bonding agent. In some instances a mild acid etching can be desirable, using a muriatic acid solution and properly rinsing substrates before the coating application. Some manufacturers require a further roughing of smooth finishes, such as sandblasting, for adequate bonding.

On masonry surfaces, voids in mortar joints should be filled before coating installation.
With both masonry and concrete substrates, existing cracks should be filled with a dry mix of cementitious material sponged into cracks. Larger cracks should be sawn out, usually to a 3 4 in minimum, and packed with nonshrink material as recommended by the coating manufacturer.

Moving joints must be detailed using sealants designed to perform under the expected movement. These joints include thermal movement and differential movement joints. The cementitious material should not be applied over these joints as it will crack and “alligator” when movement occurs.

If cracks are experiencing active water infiltration, this pressure must be relieved before coating is applied. Relief holes should be drilled in a substrate, preferably at the base of the wall, to allow wicking of water, thus relieving pressure in the remainder of work areas during coating application. After application and proper curing time (approximately 48–72 hours), drainage holes may then be packed with a nonshrink hydraulic cement material and finished with the cementitious coating.

After substrate preparations are completed and just before application, substrates must be wetted or dampened with clean water for adequate bonding of the coating. Substrates must be kept continually damp in preparation for application. The amounts of water used are dependent on weather and substrate conditions. For example in hot, dry weather, substrates require frequent wettings. Coatings should not be applied in temperatures below 40°F or in conditions when the temperature is expected to fall below freezing within 24 hours after application.

Cementitious coatings should be carefully mixed following the manufacturer’s recommended guidelines concerning water ratios. Bonding agents should be added as required with no other additives or extenders, such as sand, used unless specifically approved by the manufacturer. With smooth surfaces such as precast concrete, an additional bonding agent is required.

Cementitious coatings may be applied by brush, trowel, or spray. Stiff, coarse, or fiber brushes are used for application. Brush applications require that the material be scrubbed into a substrate, filling all pores and voids. Finish is completed by brushing in one direction for uniformity.

Spray applications are possible by using equipment designed to move the material once mixed. Competent mechanics trained in the use of spray equipment and technique help ensure acceptable finishes and watertightness (Fig. 3.11).

FIGURE 3.11 Spray application of cementitious membrane on negative side.

Trowel applications are acceptable for the second coat of material. Due to the application thickness of this method, manufacturers recommend that silica sand be added to the mix in proper portions. The first coats of trowel applications are actually brush applications that fill voids and pores. Finish trowel coats can be on a continuum from smooth to textured. Sponge finishing of the first coat is used to finish smooth concrete finishes requiring a cementitious application.

With textured masonry units such as split face or fluted block, additional material is required for effective waterproofing. On this type of finish, spraying or brush applications are the only feasible and effective means.

The amount of material required depends upon the expected water conditions. Under normal waterproofing requirements, the first coat is applied at a rate of 2 pounds of material per square yard of work area. The finish coat is then applied at a coverage rate of 1 lb/yd2. In severe water conditions, such as below-grade usage with water-head pressures, materials are applied at 2 lb/yd^2. This is followed by a trowel application at 2 lb/yd2. Clean silica sand is added to the second application at 25 lb of silica to one bag, 50 lb, of premixed cementitious coating.

With all applications, the second material coat should be applied within 24 hours after applying the first coat. Using these application rates, under normal conditions, a 50-pound bag of coating will cover approximately 150 ft 2 (1 lb/yd2 , first coat; 2 lb/yd2 , second coat). The finish thickness of this application is approximately  1 /8 in.

Trying to achieve this thickness in one application, or adding excessive material thickness in one application, should not be attempted. Improper bonding will result, and material can become loose and spall. To eliminate mortar joint shadowing on a masonry wall being visible through the coating, a light trowel coat application should be applied first, followed by a regular trowel application.

The cementitious coating beginning to roll or pull off a substrate is usually indicative of the substrate being too dry; redampening with clean water before proceeding is necessary. Mix proportions must be kept constant and uniform, or uneven coloring or shadowing of the substrate will occur.

After cementitious coatings are applied they should be cured according to the manufacturer’s recommendations. Typically, this requires keeping areas damp for 1–3 days. In extremely hot weather, more frequent and longer cure times are necessary to prevent cracking of the coating. The water cure should not be done too soon after application, as it may ruin or harm the coating finish. Chemical curing agents should not be used or added to the mix unless specifically approved by the coating manufacturer.

Typically, primers are not required for cementitious coating applications, but bonding agents are usually added during mixing. In some cases, if substrates are especially smooth or previous coatings have been removed, a direct application of the bonding agent to substrate surfaces is used as a primer. If there is any question regarding bonding strength, samples should first be applied both with and without a bonding agent and tested before proceeding with the complete application.

Cementitious coatings should not be applied in areas where thermal, structural, or differential movement will occur. Coatings will crack and fail if applied over sealant in control or expansion joints. Cementitious-based products should not be applied over substrates other than masonry substrates such as wood, metal, or plastics,

Paints and elastomeric coatings are similar in that they always contain three basic elements in a liquid state: pigment, binder, and solvent. In addition, both often contain special additives such as mildew-resistant chemicals. However, paints and coatings differ in their intended uses.

Paints are applied only to add decorative color to a substrate. Coatings are applied to water- proof or otherwise protect a substrate. The difference between clear sealers and paints or coatings is that sealers do not contain the pigments that provide the color of paints or coatings.

Solvent is added to paints and coatings to lower the material viscosity so it can be applied to a substrate by brush, spray, or roller. The binder and solvent portion of a paint or coating is referred to as the vehicle. A coating referred to as 100 percent solids is merely a binder in a liquid state that cures, usually moisture cured from air humidity, to a seamless film upon application. Thus it is the binder portion, common to all paints and coatings, that imparts the unique characteristics of the material, differentiating coatings from paints.

Waterproof coatings are classified generically by their binder type. The type of resin materials added to the coating imparts the waterproofing characteristics of the coating material. Binders are present in the vehicle portion of a coating in either of two types. An emulsion occurs when binders are dispersed or suspended in solvent for purposes of application. Solvent-based materials have the binder dissolved within the solvent.

The manner in which solvents leave a binder after application depends upon the type of chemical polymer used in manufacturing. A thermoplastic polymer coating dries by the solvent evaporating and leaving behind the binder film. This is typical of water-based acrylic elastomeric coatings used for waterproofing. A thermosetting polymer reacts chemically or cures with the binder and can become part of the binder film that is formed by this reaction. Examples are epoxy paints, which require the addition and mixing of a catalyst to promote chemical reactions for curing the solvent.

The catalyst prompts a chemical reaction that limits application time for these materials before they cure in the material container. This action is referred to as the “pot life” of material (workability time). The chemical reactions necessary for curing create thermosetting polymer vehicles that are more chemically resistant than thermoplastic materials.

Thermosetting vehicles produce a harder film and have an ability to contain higher solids content than thermoplastic materials.

Resins used in elastomeric coatings are breathable. They allow moisture-vapor trans- mission from the substrate to escape through the coating without causing blisters in the coating film. This is a favorable characteristic for construction details at undersides of bal- conies that are subjected to negative moisture drive. Thermosetting materials such as epoxy paints are not breathable. They will blister or become unbonded from a substrate if subjected to negative moisture drive.

Resins

Elastomeric coatings are manufactured from acrylic resins with approximately 50 percent solids by volume. Most contain titanium dioxide to prevent chalking during weathering.

Additional additives include mildewcides, alkali-resistant chemicals, various volume extenders to increase solids content, and sand or other fillers for texture. Resins used in waterproofing coatings must allow the film to envelop a surface with sufficient dry film millage (thickness of paint measured in millimeters) to produce a film that is watertight, elastic, and breathable. Whereas paints are typically applied 1–4 mil thick, elastomeric coatings are applied 10–20 mil thick.

It is this thickness (with the addition of resins or plasticizers that add flexibility to the coating) that creates the waterproof and elastic coating, thus the term elastomeric coating.

Elastomeric coatings have the ability to elongate a minimum of 300 percent at dry millage thickness of 12–15 mil. Elongation is tested as the minimum ability of a coating to expand and then return to its original shape with no cracking or splitting (tested according to ASTM D-2370). Elongation should be tested after aging and weathering to check effec- tiveness after exposure to the elements.

Elastomeric coatings are available in both solvent-based and water-based vehicles.  Water-based vehicles are simpler to apply and not as moisture-sensitive as the solvent- based vehicles. The latter are applied only to totally dry surfaces that require solvent materials for cleanup.

Typical properties of a high-quality, waterproof, and elastic coating include the following:

● Minimum of 10-mil dry application
● High solids content (resins)
● Good ultraviolet weathering resistance
● Low water absorption, withstanding hydrostatic pressure
● Permeability for vapor transmission
● Crack-bridging capabilities
● Resistance to sulfites (acid rain) and salts
● Good color retention and low dirt pickup
● High alkali resistance

Acrylic coatings are extremely sensitive to moisture during their curing process, taking up to 7 days to cure. Should the coating be subjected to moisture during this time, it may reemulsify (return to liquid state). This becomes a critical installation consideration when- ever such coatings are used in a horizontal or slightly inclined surface that might be susceptible to ponding water.

Elastomeric coating installations

Elastomeric coatings, which are used extensively on stucco finish substrates and exterior insulation finish systems (EIFS), are also used on masonry block, brick, concrete, and wood substrates. Some are available with asphalt primers for application over asphalt finishes. Others have formulations for use on metal and sprayed urethane foam roofs.

Elastomeric coatings are also successfully used over previously painted surfaces. By cleaning, preparing the existing surface, repairing cracks (Fig. 3.12), and priming, coatings can be used to protect concrete and masonry surfaces that have deteriorated through weathering and aging (Fig. 3.13).

FIGURE 3.12 Preparation of substrate including crack repair prior to elastomeric coating application.

FIGURE 3.13 Application of elastomeric coating

Proper preparation, such as tuck-pointing loose and defective mortar joints and injecting epoxy into cracks, must be completed first. In single-wythe masonry construction, such as split-face block, applying a cementitious block filler is necessary to fill voids in the block before applying elastomeric coating for effective waterproofing.

Aesthetically, coatings are available in a wide range of textures and are tintable to any imaginable color. However, deep, dark, tinted colors may fade, or pigments added for coloring may bleed out creating unsightly staining. Heavy textures limit the ability of a coating to perform as an elastomeric due to the amount of filler added to impart texture.

Because elastomeric coatings are relatively soft materials (lower tensile strength to impart flexibility), they tend to pick up airborne contaminants. Thus lighter colors, including white, may get dirty quickly.

Uniform coating thickness is critical to ensure crack bridging and thermal movement capabilities after application. Applicators should have wet millage gages for controlling the millage of coating applied.

Applications of elastomeric coatings are extremely labor-sensitive. They require skilled application of the material. In addition, applicators must transition coating applications into adjacent members of the building envelope, such as window frames and flashings, for effective envelope waterproofing. (See Table 3.13.)

Wood: A Renewable Resource

Wood is the only major structural material that is renewable.

In the United States and Canada, tree growth each year  greatly exceeds the volume of harvested trees, though many timberlands are not managed in a sustainable manner.

On other continents, many countries long ago felled the  last of their forests, and many forests in other countries are  being depleted by poor management practices and slash- and-burn agriculture. Particularly in the case of tropical  hardwoods, it is wise to investigate sources and to ensure  that the trees were grown in a sustainable manner.

Some panel products can be manufactured from rapidly  renewable vegetable fibers, recoverable and recycled wood  bers, or recycled cellulose fibers.

Bamboo, a rapidly renewable grass, can replace wood in  the manufacture of ß ooring, interior paneling, and other nish carpentry applications. In other parts of the world,  bamboo is used for the construction of scaffolding, concrete formwork, and even as the source off  brous material for structural panels analogous to wood-based oriented  strand board (OSB), particleboard, and fiberboard.

Forestry Practices

Two basic forms of forest management are practiced  in North America: sustainable forestry, and clearcutting  and replanting. The clearcutting forest manager attains  sustainable production by cutting all the trees in an area,  leaving the stumps, tops, and limbs to decay and become  compost, setting out new trees, and tending them until  they are ready for harvest. In sustainable forestry, trees are  harvested more selectively from a forest in such a way as to  minimize damage to the forest environment and maintain  the biodiversity of its natural ecosystem.

Environmental problems often associated with logging of forests include loss of wildlife habitat, soil erosion, pollution of waterways, and air pollution from machinery ex- hausts and burning of tree wastes. A recently clearcut forest  is a shockingly ugly tangle of stumps, branches, tops, and  substandard logs left to decay. It is crisscrossed by deeply rutted, muddy haul roads. Within a few years, decay of the  waste wood and new tree growth largely heal the scars. Loss  of forest area may raise levels of carbon dioxide, a greenhouse gas, in the atmosphere, because trees take up carbon  dioxide from the air, utilize the carbon for growth, and give
back pure oxygen to the atmosphere.

The buyer of wood products can support sustainable forestry practices by specifying products certified as originating from sustainable forests, those that are managed in  a socially responsible and environmentally sound manner. 

FSC-certified wood products, for example, satisfy the  requirements of LEED and all other major green building  assessment programs.

Mill Practices

Skilled sawyers working with modern computerized sys- tems can convert a high percentage of each log into marketable wood products. A measure of sawmill performance is  the lumber recovery factor (LRF), which is the net volume  of wood products produced from a cubic meter of log.

Manufactured wood products such as oriented strand  board, particleboard, I-joists, and laminated strand lumber effciently utilize most of the wood fiber in a tree and  can be produced from recycled or younger-growth, rapidly renewable materials; finger-jointed lumber is made  by gluing end to end short pieces of lumber that might  otherwise be treated as waste. The manufacturer of large,  solid timbers generates more unused waste and yields fewer  products from each log.

Kiln drying uses large amounts of fuel but produces  more stable, uniform lumber than air drying, which uses  no fuel other than sunlight and wind.

Mill wastes are voluminous: Bark may be shredded to  sell as a landscape mulch, composted, burned, or buried in  a landfill. Sawdust, chips, and wood scraps may be burned  to generate steam to power the mill, used as livestock bedding, composted, burned, or buried in a land.

Many wood products can be manufactured with significant percentages of recoverable or recycled wood, plant ber, or paper materials.

Transportation

Because the major commercial forests are located in  concentrated regions of the United States and Canada,  most lumber must be shipped considerable distances.

Fuel consumption is minimized by planing and drying the lumber before it is shipped, which reduces both weight  and volume.

Some wood products can be harvested or manufactured  locally or regionally.

Energy Content

Solid lumber has an embodied energy of roughly 1000 to  3000 BTU per pound (2.3 to 7.0 MJ/kg). An average 8-foot-long 2 4 (2.4-m-long 38 89 mm) has an embodied energy  of about 17,000 BTU (40 MJ).
This includes the energy ex- pended to fell the tree, transport the log, saw and surface the  lumber, dry it in a kiln, and transport it to a building site.

Manufactured wood products have higher embodied  energy content than solid lumber, due to the glue and resin  ingredients and the added energy required in their manu- facture. The embodied energy of such products ranges from  about 3000 to 7500 BTU per pound (7.0 to 17 MJ/kg).

Wood construction involves large numbers of steel fas- teners of various kinds. Because steel is produced by relatively energy-intensive processes, fasteners add considerably  to the total energy embodied in a wood frame building.

Wood does not have the lowest embodied energy of the  major structural materials when measured on a pound-for-pound basis. However, when buildings of comparable size, but  structured with either wood, light gauge steel studs, or concrete, are compared, most studies indicate that those of wood  have the lowest total embodied energy of the three. This is  due to woodÕs lighter weight (or, more precisely, its lesser density) in comparison to these other materials, as well as the rela- tive efficiency of the wood light frame construction system.

Construction Process

A significant fraction of the lumber delivered to a construction site is wasted: It is cut off when each piece is sawed to size and shape and ends up on the scrap heap, which is  usually burned or taken to a landfill. On-site cutting of lumber also generates considerable quantities of sawdust. Construction site waste can be reduced by designing buildings that utilize full standard lengths of lumber and full sheets  of wood panel materials.

Wood construction lends itself to various types of prefabrication that can reduce waste and improve the efficiency of material usage in comparison to on-site building methods.


Indoor Air Quality (IAQ)

Wood itself seldom causes IAQ problems. Very few people are sensitive to the odor of wood.

Some of the adhesives and binders used in glue-laminated lumber, structural composite lumber, and  wood panel products can cause serious IAQ problems by  giving off volatile organic compounds such as formalde-hyde. Alternative products with low-emitting binders and  adhesives are also available.

Some paints, varnishes, stains, and lacquers for wood  also emit fumes that are unpleasant and/or unhealthful.

In damp locations, molds and fungi may grow on wood  members, creating unpleasant odors and releasing spores  to which many people are allergic.

Building Life Cycle

If the wood frame of a building is kept dry and away  from fire, it will last indefinitely. However, if the building is  poorly maintained and wood elements are frequently wet,  wood components may decay and require replacement.

Wood is combustible and gives off toxic gases when it  burns. It is important to keep sources of ignition away from  wood and to provide smoke alarms and easy escape routes  to assist building occupants in escaping from burning buildings. Where justified by building size or type of occupancy,  building codes require sprinkler systems to protect against  the rapid spread of fire.

When a building is demolished, wood framing members  can be recycled directly into the frame of another building, sawn into new boards or timbers, or shredded as raw  material for oriented-strand materials. There is a growing  industry whose business is purchasing and demolishing  old barns, mills, and factories and selling their timbers as  reclaimed lumber.

A study commissioned by the Canadian Wood Council compares the full life cycle of three similar office buildings, one each framed with wood, steel, or concrete and all  three operated in a typical Canadian climate. In this study,  total embodied energy for the wood building is about half  of that for the steel building and two-thirds of that for the  concrete building. The wood building also outperforms  the others in measures of greenhouse gas emissions, air pollution, solid waste generation, and ecological impact.

Successful application of elastomeric coatings depends entirely on proper substrate preparation. Although they are effective waterproof materials, they should not be applied over cracks, voids, or deteriorated materials, as this will prevent cohesive waterproofing of the building envelope. Coatings chosen must be compatible with any existing coatings, sealants, or patching compounds used in crack repairs. Coating manufacturers have patching, sealing, and primer materials, all compatible with their elastomeric coating.

Applying elastomeric coating requires applicator knowledge beyond a typical paint job.
Most painting contractors do not have the experience or knowledge to apply these coatings.
Existing substrates must be cleaned to remove all dirt, mildew, and other contaminants. This is accomplished by pressure-cleaning equipment with a minimum capability of 1500 lb/in2 water pressure. All grease, oils, and asphalt materials must be removed completely.

Mildew removal with chlorine should be done where necessary. Chemical cleaning is also necessary to remove traces of release agents or incompatible curing agents. If chemicals are used, the entire surface should be rinsed to remove any chemical traces that might affect the coating bonding.

Previously painted substrates should have a duct-tape test for compatibility of the elastomeric coating application. A sample area of coating should be applied over existing materials and allowed to dry. Then duct tape should be sealed firmly to the substrate then pulled off quickly. If any amount of coating comes off with the tape, coatings are not properly adhering to existing materials. In that case, all existing coatings or paints must be removed to ensure adequate bonding. No coating can perform better than the substrate to which it is applied, in this case a poorly adhered existing coating. Either excessively chalky coatings must be removed or a primer coat applied. Primers will effectively seal the surface for proper bonding to a substrate.

High-alkaline masonry substrates must be checked for a pH rating before installation.
The pH rating is a measure of substrate acidity or alkalinity. A rating of 7 is neutral, with higher ratings corresponding to higher alkaline substrates. A pH of more than 10 requires following specific manufacturer’s recommendations. These guidelines are based upon the alkali resistance of a coating and substrate pH.

Surface preparations of high-alkali substrates include acid washing with 5 percent muriatic acid or primer application. In some cases, extending curing time of concrete or stucco substrates will effectively lower their pH. Immediately after application stucco has a high pH, but it has continually lower pH values during final curing stages. New stucco should cure for a minimum of 30 days, preferably 60–90 days, to lower the pH. This also allows shrinkage and thermal cracks to form and be treated before coating application.

Sealant installation should be completed before applying elastomeric coating to prevent joint containment by the coating. This includes expansion and control joints, perimeters of doors and windows, and flashings. Small nonmoving cracks less than  1/ 16 in wide require filling and overbanding 2 in wide with a brushable or knife-grade sealant material (Fig. 3.14).

FIGURE 3.14 Crack repair, under  1⁄16 in, for elastomeric substrate preparation.

FIGURE 3.15 Crack repair, over  1⁄16 in, for elastomeric substrate preparation.

Cracks exceeding  1 /16 in that are also nonmoving joints should be sawn out to approximately a  1 4-in width and depth and filled with a knife-grade sealant, followed by overbanding approximately 4 in wide (see Fig. 3.15). Changes in direction should be reinforced as shown in Fig. 3.16.

FIGURE 3.16 Changes in envelope plane require detailing prior to elastomeric application.

Overbanding (bandage application of a sealant) requires skilled craftspeople to featheredge banding sides to prevent telescoping of patches through the coating. Thick, unfeathered applications of brushable sealant will show through coating applications, providing an unacceptable substrate appearance.

Large cracks over 1 /2 in wide that are nonmoving, such as settlement cracks, should be sawn out, and proper backing materials applied before sealant installation (Fig. 3.17).

FIGURE 3.17 Large movement crack or joint repair for elastomeric coatings.

Fiberglass mesh in 4-in widths can be embedded into the brushable sealant for additional protection.

Joints that are expected to continue moving, such as joints between dissimilar materials, should be sealed using guidelines set forth in Chap. 5. These joints should not be coated over, since the movement experienced at these joints typically exceeds the elastomeric coating capability. In such cases, the coating will alligator and develop an unsightly appearance.

Brick or block masonry surfaces should be checked for loose and unbonded mortar joints. Faulty joints should be tuck-pointed or sealed with a proper sealant. With masonry applications, when all mortar joints are unsound or excessively deteriorated, all joints should be sealed before coating.

Additionally, with split-face block, particularly single-wythe construction, a cementitious block filler should be applied to all cavities and voids. This provides the additional waterproofing protection that is necessary with such porous substrates. On previously painted split face construction, an acrylic block filler may be used to prepare the surface.

All sealants and patching compounds must be cured before coating application; if this is not done, patching materials will mildew beneath the coating and cause staining. For metal surfaces, rusted portions must be removed or treated with a rust inhibitor, then primed as rec- ommended by the coating manufacturer. New galvanized metal should also be primed.

Wood surfaces require attention to fasteners that should be recessed and sealed. Laps and joints must also be sealed. Wood primers are generally required before coating application. The success of an elastomeric coating can depend upon use of a proper primer for specific conditions encountered. Therefore, it is important to refer to manufacturer guide-lines for primer usage.

Elastomeric coatings are applied by brush, roller, or spray after proper mixing and agitating of the coating (see Fig. 3.18). Roller application is preferred, as it fills voids and crevices in a substrate. Long nap rollers should be used with covers having a  3 4–1 2-in nap. Elastomeric coatings typically require two coats to achieve proper millage. The first application must be completely dried before the second coat is applied.

FIGURE 3.18 Elastomeric coating application after preparatory work is completed.

Spray applications require a mechanic properly trained in the crosshatch method. This method applies coating by spraying vertically and then horizontally to ensure uniform coverage. Coatings are then back-rolled with a saturated nap roller to fill voids and crevices.

Brushing is used to detail around windows or protrusions, but it is not the preferred method for major wall areas. When using textured elastomeric coatings, careful application is extremely important to prevent unsightly buildup of texture by rolling over an area twice. Placing too much pressure on a roller nap reduces the texture applied and presents an unsightly finish. Textured application should not be rolled over adjacent applications, as roller seams will be evident after drying.

Coatings, especially water-based ones, should not be applied in temperatures lower than 40°F and should be protected from freezing by proper storage. Manufacturers do not recommend application in humidity over 90 percent. Application over excessively wet substrates may cause bonding problems. In extremely hot and dry temperatures, substrates are misted to prevent premature coating drying. Complete curing takes 24–72 hours; coatings are usually dry to the touch and ready for a second coat in 3–5 hours, depending on the weather.

Coverage rates vary depending upon the substrate type, porosity of the substrate, and millage required. Typically, elastomeric coatings are applied at 100–150 ft^2  /gal per coat, for a net application of 50–75 ft^2
/ gal. This results in a dry film thickness of 10–12 mil.

Elastomeric coatings should not be used in below-grade applications where they can reemulsify and deteriorate, nor are they designed for horizontal surfaces subject to traffic.

Horizontal areas such as copings or concrete overhangs should be checked for ponding water that may cause debonding and coating reemulsification (Fig. 3.19).

FIGURE 3.19 Reemulsification of coating.

Several choices are available for effective waterproofing of horizontal portions of a building envelope. Several additional choices of finishes or wearing surfaces over this waterproofing are also available. Liquid-applied seamless deck coatings or membranes are used where normal roofing materials are not practical or acceptable. Deck coatings may be applied to parking garage floors, plaza decks, balcony decks, stadium bleachers, recreation roof decks, pool decks, observation decks, and helicopter pads. In these situations, waterproof coatings occupy areas beneath the decks and provide wearing surfaces acceptable for either vehicular or pedestrian traffic. These systems do not require topping slabs or protection such as tile pavers to protect them from traffic.

Deck coatings make excellent choices for remedial situations where it is not possible to allow for the addition of a topping slab or other waterproofing system protection. Deck coatings are installed over concrete, plywood, or metal substrates, but should not beinstalled over lightweight insulating concrete.

Deck coatings are also used to protect concrete surfaces from acid rain, freeze–thaw cycles, and chloride ion penetration, and to protect reinforcing steel.

In certain situations, deck coatings are not specifically installed for their waterproofing characteristics but for protection of concrete against environmental elements. For example,


whereas deck coatings on the first floor of a parking garage protect occupied offices on ground level, they also protect concrete against road salts and freeze–thaw cycles on all other levels. In these situations, coatings are installed to prevent unnecessary maintenance costs and structural damage during structure life-cycling.

Deck coatings are usually installed in two- to four-step applications, with the final coat containing aggregate or grit to provide a nonslip wearing surface for vehicular or foot traffic. Aggregate is usually broadcast into the final coat either by hand seeding or by mechanical spray such as sandblast equipment. Aggregates include silica sand, quartz carbide, aluminum oxide, or crushed walnut shells. The softer, less harsh silica sand is used for pedestrian areas; the harder-wearing aggregate is used for vehicular traffic areas. The amount of aggregate used varies, with more grit concentrated in areas of heavy traffic such as parking garage entrances or turn lanes.

Due to the manufacturing processes involved, deck coatings are available in several standard colors but usually not in custom colors. A standard gray color is recommended for vehicular areas because oils and tire trackings will stain lighter colors. Some manu- facturers allow their coatings to be color-top-coated with high-quality urethane coatings, if a special color is necessary, but only in selected cases and not in vehicular areas.

Deck coatings are supplied in two or three different formulations for base, intermediate, and wearing coats. Base coats are the most elastomeric of all formulations. Since they are not subject to wear, they do not require the high tensile strength or impact resistance that wearing layers require. Lower tensile strength allows a coating to be softer and, there- fore, to have more elastomeric and crack-bridging characteristics than topcoats. As such, base coats are the waterproof layer of deck-coating systems.

Top and intermediate coats are higher in tensile strength and are impact-resistant to withstand foot or vehicular traffic. However, the various coating layers must be compatible and sufficiently similar to base coat properties not to crack or alligator as a paint applied over an elastomeric coating might. This allows base coatings to move sufficiently to bridge cracks that develop in substrates without cracking topcoats.

Adding grit or aggregate in a coating further limits movement capability of topcoats.

The more aggregate added, the less movement topcoats can withstand, further restricting movement of base coats.

Deck coatings are available in several different chemical formulations. They are differ- entiated from clear coatings, which are penetrating sealers, in that they are film-forming surface sealers. Deck coating formulations include the following:

● Acrylics
● Cementitious coatings
● Epoxy
● Asphalt overlay
● Latex
● Neoprene
● Hypalon
● Urethane
● Modified urethane
● Sheet systems

Acrylics

Acrylics are not waterproof coatings, but act as water-repellent sealers. Their use is primarily aesthetic, to cover surface defects and cracking in decks. These coatings have low elastomeric capabilities; silica aggregate is premixed directly into their formulations, which further lowers their elastic properties. These two characteristics prevent acrylics from being true waterproof coatings.

The inherent properties of acrylics protect areas such as walkways or balconies with no occupied areas beneath from water and chloride penetration. In addition to concrete sub- strates, acrylics are used over wood or metal substrates, provided that recommended primers are installed. Acrylics are also used at slab-on-grade areas where urethane coatings are not recommended.

Sand added in acrylic deck coatings provides excellent antislip finishes. As such, they are used around pools or areas subject to wet conditions that require protection against slips and falls. Acrylics are not recommended for areas subject to vehicular traffic. Some manufacturers allow their use over asphaltic pavement subject only to foot traffic, for aesthetics and a skid-resistant finish. (See Table 3.14.)


Cementitious

Cementitious deck coatings are used for applications over concrete substrates and include an abrasive aggregate for exposure to traffic. These materials are supplied in prepacked and premixed formulations requiring only water for mixing. Cementitious coatings are applied by trowel, spray, or squeegee, the latter being a self-leveling method.

Cementitious systems contain proprietary chemicals to provide necessary bonding and waterproofing characteristics. These are applied to a thickness of approximately  1 8 in and will fill minor voids in a substrate. A disadvantage of cementitious coatings, like below- grade cementitious systems, is their inability to withstand substrate movement or cracking.

They are one-step applications, with integral wearing surfaces, which require no primers and are applicable over damp concrete surfaces.

Modified acrylic cementitious coatings are also available. Such systems typically include a reinforcing mesh embedded into the first coat to improve crack-bridging capabilities. Acrylics are added to the basic cement and sand mixture to improve bonding and performance characteristics.

Cementitious membrane applications include the dry-shake and power-trowel methods previously discussed in Chap. 2. Successful applications depend on properly designed, detailed, and installed allowances for movement, both thermal and differential. For cementitious membranes to be integrated into a building envelope, installations should include manufacturer-supplied products for cants, patching, penetrations, and terminations. (See Table 3.15.)


Epoxy

As with acrylics, epoxy coatings are generally not considered true waterproof coatings.
They are not recommended for exterior installations due to their poor resistance to ultraviolet weathering. Epoxy floor coatings have very high tensile strengths, resulting in low elastomeric capabilities. These coatings are very brittle and will crack under any movement, including thermal and structural.

Epoxy coatings are used primarily for interior applications subject to chemicals or harsh conditions such as waste and water treatment plants, hospitals, and manufacturing facilities. For interior applications not subject to movement, epoxy floor coatings provide effective waterproofing at mechanical room floor, shower, and locker room applications.

Epoxy coatings are available in a variety of finishes, colors, and textures, and may be roller- or trowel-applied.

Epoxy deck coatings are also used as top coats over a base-coat waterproof membrane of urethane or latex. However, low-movement capabilities and brittleness of epoxy coatings limit elastomeric qualities of waterproof top coats. (See Table 3.16.)


Asphalt

Asphalt overlay systems provide an asphalt wearing surface over a liquid-applied membrane. The waterproofing base coat is a rubberized asphalt or latex membrane that can withstand the heat created during installation of the asphalt protective course. Both the waterproof membrane and the asphalt layers are hot-applied systems.

Asphalt layers are approximately 2 in thick. These systems have better wearing capabilities due to the asphaltic overlay protecting the waterproof base coating.

The additional weight added to a structure by these systems must be calculated to ensure that an existing parking garage can withstand the additional dead loads that are created.

Asphalt severely restricts the capability of the waterproof membrane coating to bridge cracks or to adjust to thermal movement. Additionally, it is difficult to repair the waterproofing membrane layers once the asphalt is installed. There is no way to remove overlays without destroying the base coat membrane. Asphaltic systems are not recoatable. For maintenance, they must be completely removed and reinstalled. (See Table 3.17.)



Latex, neoprene, hypalon

Deck coatings are available in synthetic rubber formulations, including latex, neoprene, neoprene cement, and hypalon. These formulations include proprietary extenders, pigments, and stabilizers. Neoprene derivatives are soft, low-tensile materials and require the addition of a fabric or fiberglass reinforcing mesh. For traffic-wear resistance, this reinforcing mesh enhances in-place performance properties such as elongation and crack-bridging capabilities.

Reinforcing requires that the products be trowel applied rather than roller or squeegee applied.
Trowel application and a finish product thickness of approximately  1 4 in increase the in-place costs of these membranes. They also require experienced mechanics to install the rubber derivative systems. Trowel applications, various derivatives, and proprietary formulations provide designers with a wide range of textures, finishes, and colors.

Rubber compound coatings have better chemical resistance than most other deck-coating systems. They are manufactured for installation in harsh environmental conditions such as manufacturing plants, hospitals, and mechanical rooms. They are appropriate in both exterior and interior applications.

Design allowances must be provided for finished application thickness. Deck protrusions, joints, wall-to-floor details, and equipment supports must be flashed and reinforced for membrane continuity and watertightness. Certain derivatives of synthetic rubbers become brittle under aging and ultraviolet weathering, which hinders waterproofing capabilities after installation. Manufacturer’s literature and applicable test results should be reviewed for appropriate coating selection. (See Table 3.18.)


Urethanes

Urethane deck coatings are frequently used for exterior deck waterproofing. These are available for both pedestrian and vehicular areas in a variety of colors and finishes. Urethane systems include aromatic, aliphatic, and epoxy-modified derivatives and formulations.

Aliphatic materials have up to three times the tensile strength of aromatics but only 50 percent of aromatic elongation capability. Many manufacturers use combinations of these two materials for their deck-coating systems. Aromatic materials are installed as base coats for better movement and recovery capabilities; aliphatic urethane top coats make for better weathering, impact resistance, and ultraviolet resistance.

Epoxy urethane systems are also used as top coat materials. These modified urethane systems provide additional weathering and wear, while still maintaining necessary waterproofing capabilities.

Urethane coatings are applied in two or more coats, depending upon the expected traffic wear. Aggregate is added in the final coating for a nonslip wearing surface. An installation advantage with urethane systems is their self-flashing capability. Liquid-applied coatings by brush application are turned up adjoining areas at wall-to-floor junctions, piping penetrations, and equipment supports and into drains.

Urethane coatings are manufactured in self-leveling formulations for applications control of millage on horizontal surfaces. Nonflow or detailing grades are available for vertical or sloped areas. The uncured self-leveling coating is applied by notched squeegees to control thickness on horizontal areas. At sloped areas, such as the up and down ramps of parking garages or vertical risers of stairways, nonflow material application ensures proper millage. If self-leveling grade is used in these situations, material will flow downward and insufficient millage at upper areas of the vertical or sloped portions will occur.

Nonflow liquid material is used to detail cracks in concrete decks before deck-coating application. Cracks wider than  1 /16 in, which is the maximum width that urethane materials bridge without failure, are sawn out and sealed with a urethane sealant. This area is then detailed 4 in wide with nonflow coating.

In addition, urethane coatings are compatible with urethane sealants used for cants between vertical and horizontal junctions, providing a smooth transition in these and other changes of  plane. This is similar to using wood cants for roof perimeter details (see Table 3.19).

While they do not fit the description of a deck coating per se, there are balcony and deck waterproofing systems that are available in sheet materials that provide waterproofing capabilities. There are a variety of systems available, including those that require the sheet embedded in a trowel- or spray-applied acrylic or resin material, and those that are act as a complete system.

The latter is a vinyl product, similar to a typical interior vinyl flooring product with the exception that the product is improved to withstand exterior weathering and of course water infiltration. The system is vulnerable for leakage at the seams, following the 90%/1% principle. If seaming is adequately addressed, including the necessary vertical turn-ups, the product can be an effective barrier system. These systems make excellent candidates for remedial application, as they can hide considerably more substrate imperfections than the liquid systems discussed previously. These systems can also be applied to wood substrates and make excellent choices for residential applications including apartment projects.

Many systems combine the properties of the liquid-applied systems with sheet good reinforcing for “belt and suspenders” protection. The limiting factor is cost, as the more material and layers a system requires for effectiveness, the more the final in-place cost rises. Table 3.20 summaries the advantages and disadvantages of using sheet systems for waterproofing applications.

Deck coatings bond directly to concrete, wood, or metal substrates. This prevents lateral movement of water beneath the coatings, as is possible with sheet good systems. Once cured, coatings are nonbreathable and blister if negative vapor drive is present. This is the reason deck coatings, with the exception of acrylic and epoxies, are not recommended for slab-on-grade applications. Specifically, moisture in soils is drawn up into a deck by capillary action, causing blistering in applied deck coatings. In the same manner, blistering occurs in deck coatings applied on upper deck portions of sandwich-slab membranes due to entrapped moisture and negative vapor drive. In both cases, an epoxy vapor barrier prime coat should be installed to protect deck-coating systems from being subjected to this vapor drive.

Physical properties of deck coatings vary as widely as the number of systems available. Important considerations to review when choosing a coating system include tensile strength, elongation, chemical resistance, weathering resistance, and adhesion properties. Different installation types, expected wearing, and weathering conditions require different coating types.

High tensile strength is necessary when a coating is subject to heavy wear including vehicular traffic or forklift traffic at loading docks. Tensile strengths of some deck coatings exceed 1000 lb/in^2 (tested according to ASTM D-412) and are higher for epoxy coatings. This high tensile strength reduces the elongation ability of coatings.

Elongation properties range from 200 percent (for high-tensile-strength top coats) to more than 1000 percent (for low-tensile-strength base coats). For pedestrian areas where impact resistance and heavy wear is not expected, softer, higher elongation aromatic ure- thanes are used. Sun decks subject to impact from lawn chairs and tables would be better served by a coating between the extremes of high and low tensile strength.

Chemical resistance can be an important consideration under certain circumstances.
Parking garage decks must have coatings resistant to road salts, oil, and gasoline. A pedes- trian sun deck may be subjected to chlorine and other pool chemicals. Testing for chemical resistance should be completed according to recognized tests such as ASTM D-471.

Weathering resistance and ultraviolet resistance are important to coatings exposed to the elements such as on upper levels of a parking garage. These areas should be protected by the ultraviolet-resistant properties of coatings such as an aliphatic urethane. Weathering characteristics can be compared with accelerated weathering tests such as ASTM D-822.

Other properties to consider on an as-needed basis include adhesion tests, solvent odor for interior uses, moisture vapor transmission, and fire resistance.

Once installed, the useful life of deck coatings depends upon proper maintenance as well as traffic wear. Heavily traveled parking garage decks and loading docks will wear faster than a seldom-used pedestrian deck area. To compensate, manufacturers recommend a minimum of one to as many as three additional intermediate coat applications. Additional aggregate is also added for greater wear resistance (Fig. 3.20).

FIGURE 3.20 Suggested aggregate texture layout for maximum protection of deck coating.

With proper installation, deck coatings should function for upward of 5 years before requiring resealing. Resealing entails cleaning, patching existing coatings as required, reapplying top coatings, and, if required, adding intermediate coats at traffic lanes. Proper maintenance prevents coatings from being worn and exposing base coatings that cannot withstand traffic or exposure.

Exposed and unmaintained deck-coating systems require complete removal and replacement when repairs become necessary. Chemical spills, tears or ruptures, and improper usage must also be repaired to prevent unnecessary coating damage. Maintaining the top coat or wearing surface properly will extend the life cycle of a deck-coating system indefinitely.

Deck coatings are also effective in remedial waterproofing applications. If a sandwich- slab membrane installed during original construction becomes ineffective, a deck coating can be installed over the topping slab provided proper preparatory work is completed.

Deck coatings can also be successfully installed over quarry and other hard-finish tile sur- faces, precast concrete pavers, and stonework. With any special surfacing installation, proper adhesive tests and sample applications should be completed.

When deck coatings are being applied at a job site, it is the only time when golf shoes are mandatory attire! Liquid deck coatings are required to be squeegee-applied to ensure sufficient and uniform millage. The millage rate is too thick for spray applications, which cannot also provide the uniform thickness required.

During application the squeegee is pushed, not pulled, to prevent the blade end of the squeegee from being pulled down too hard against the substrate and applying too thin a wet millage of material. Pushing of the squeegee blade maintains the blade in an upright position and a uniform millage application.

This pushing of the squeegee requires that the mechanic walk through the applied material, thus requiring the golf shoes so as not to damage the installation and have shoes stick to the wet membrane. The material self-levels after installation, so that any minute impressions the golf-shoe spikes leave are quickly covered by the material.

Most deck coatings also require that the material be immediately back-rolled after initial squeegee application to further ensure uniformity of millage. These applicators must also wear the golf shoes, as do those applying the aggregate that forms the wearing surface in the top coat applications. Figure 3.21 pictures the application process of a typical deck coating application.

FIGURE 3.21 Deck-coating application. Note the pushing of squeegees in the background, back-rolling of coating and spreading of the aggregate by hand in the foreground. All crew members are wearing golf shoes.

Substrate adhesion and proper substrate finishing are critical for successful deck-coating applications. In general substrates must be clean, dry, and free of contaminants. Concrete substrates exhibiting oil or grease contamination should be cleaned with a biodegradable degreaser such as trisodium phosphate. Contaminants such as parking-stall stripe paint should be removed by mechanical grinder or sandblasting (Figs. 3.22 and 3.23).

FIGURE 3.22 Mechanical removal of contaminants.

FIGURE 3.23 Substrate has been scarified prior to deck-coating application to ensure proper adhesion.

For new concrete substrates, a light broom finish is desirable. Surface laitance, fins, and ridges must be removed. Honeycomb and spalled areas should be patched using an acceptable nonshrink grout material.

Coatings should not be applied to exposed aggregate or reinforcing steel. If present, these areas should be properly repaired. Concrete surfaces, including patches, should be cured a minimum of 21 days before coating application. Use of most curing compounds is prohibited by coating manufacturers, since resins contained in curing compounds preventadequate adhesion. If present, substrates require preparatory work, including sandblasting, or acid etching with muriatic acid. Water curing is desirable, but certain manufacturers allow use of sodium silicate curing agents.

Substrate cracks must be prepared before coating application (Fig. 3.24). Cracks less than 1 16 in wide should be filled and detailed with a 4-in band of nonflow base coat. Larger cracks, from  1 2 in to a maximum of 1-in width, should be sawn out and filled with ure- thane sealant (Fig. 3.25). Moving joints should have proper expansion joints installed with coating installed up to but not over these expansion joints. Refer to Figs. 3.26 and 3.27 for typical expansion joint detailing.

Substrates should be sloped, to drain water toward scuppers or deck drains. Plywood surfaces should be swept clean of all dirt and sawdust. Plywood should be of A-grade only, with tongue and groove connections (Fig. 3.28). Only screw-type fasteners should be used, and they should be countersunk. The screw head is filled with a urethane sealant and troweled flush with the plywood finish (Fig. 3.29). As these coatings are relatively thin, 60–100 mil dry film, their finish mirrors the substrate they are applied over.

Therefore, if plywood joints are uneven or knots or chips are apparent in the plywood, they also will be apparent in the deck-coating finish.

FIGURE 3.24 Crack repair prior to deck-coating application.

FIGURE 3.29 Deck-coating details for plywood deck applications.

Metal surfaces require sandblasting or wire-brush cleaning, then priming immediately afterward (Fig. 3.30). Aluminum surfaces also require priming (Fig. 3.31). Other substrates such as PVC, quarry tile, and brick pavers should be sanded to roughen the surface for adequate adhesion. Sample test areas should be completed to check adhesion on any of these substrates before entire application.



For recoating over previously applied deck coatings, existing coatings must be thoroughly cleaned with a degreaser to remove all dirt and oil. Delaminated areas should be cut out and patched with base coat material. Before reapplication of topcoats, a solvent is applied to reemulsify existing coatings for bonding of new coatings.

All vertical abutments and penetrations should be treated by installing a sealant cove, followed by a detail coat of nonflow material (Figs. 3.32, 3.33, and 3.34). If a joint occurs between changes in plane such as wall-to-floor joints, an additional detail coat is added or reinforcement. Figures 3.35 and 3.36 show typical installation procedures for this work.

With new construction, detail coats of base coat membrane are turned up behind the facing material (e.g., brick cavity wall), followed by coating and detailing to the facing material. This allows for double protection in these critical envelope details. At doors or sliding glass doors, coating is installed beneath thresholds before installation of doors.

Figure 3.37 shows application procedures at a deck drain.

For applications over topping slabs with precast plank construction, such as double-T, a joint should be scored at every T-joint. These joints are then filled with sealant and adetail coat of material is applied allowing for differential and thermal movement. Refer to Figs. 3.38 and 3.39 for typical installation detail at these areas.

Base coats are installed by notched squeegees for control of millage, typically 25–40 mil dry film, followed by back-rolling of materials for uniform millage thickness (Fig. 3.40).

Following initial base-coat curing, within 24 hours intermediate coats, topcoats, and aggregates are installed (Fig. 3.41).

Aggregate, silica sand, and silicon car- bide are installed in intermediate or final topcoats or possibly both in heavy traffic areas. On pedestrian decks grit is added at a rate of 4–10 lb square (100 ft^2) of deck area.

In traffic lanes, as much as 100–200 lb of aggregate per square is added.

Aggregate is applied by hand seeding (broadcasting) or by mechanical means (Fig. 3.42). If aggregate is added to a topcoat, it is back-rolled for uniform thickness of membrane and grit distribution. With installations of large aggregate amounts, an initial coat with aggregate fully loaded is first allowed to dry.

Excess aggregate is then swept off, and an additional topcoat is installed to lock in the grit and act as an additional protective layer. See Fig. 3.43 for aggregate comparisons.

Intermediate coats usually range in thickness from 10 to 30 mil dry film, whereas top coats range in thickness from 5 to 20 mil. Refer to Figs. 3.44 and 3.45 for typical millage requirement. Final coats should cure 24–72 hours before traffic is allowed on the deck,paint stripping is installed, and equipment is moved onto the deck.

Approximate coverage rates for various millage requirements are shown in Table 3.21. Trowel systems are applied to considerably greater thickness than liquid-applied systems. Troweled systems range from 1 /8–1/ 4 in total thickness, depending upon the aggregate used.

Other than applications of acrylic coatings, manufacturers require primers on all substrates for improved membrane bonding to substrates. Primers are supplied for various substrates, including concrete, wood, metal, tile, stone, and previously coated surfaces. Additionally, priming of aggregate or grit is required before its installation in the  coating. Some primers must be allowed to dry completely (concrete); others must be coated over immediately (metal). In addition to primers, some decks may require an epoxy vapor barrier to prevent blistering from negative vapor drive.

Because of the volatile nature and composition of deck-coating materials, they should not be installed in interior enclosed spaces without adequate ventilation. Deck coatings are highly flammable, and extreme care should be used during installation and until fully cured. Deck coating requires knowledge- able, trained mechanics for applications, and manufacturer’s representatives should review details and inspect work during actual progress.

Figure 3.46 demonstrates proper deck coating application, and Fig. 3.47 demon- strates the various stages of deck-coating application.

Although similar to vertical surface sealers, clear horizontal sealers require a higher percentage of solids content to withstand the wearing conditions encountered at horizontal areas. Decks are subject to ponding water, road salts, oils, and pedestrian or vehicular traffic. Such in-place conditions require a solids content of 15–30 percent, depending on the number of application steps required. Typically, two coats are required for lower solids material and one coat for 30 percent solids material. In addition, complete sub- strate saturation is required rather than the spray or roller application suitable for vertical installations.

Clear wall sealers differ from elastomeric coatings in much the same way that clear deck sealers differ from deck coatings. Clear deck sealers cannot bridge cracks in a substrate, whereas most deck coatings bridge minimum cracking. Clear sealers can be applied only over concrete substrates, whereas deck coatings can be applied over metal and wood substrates. Clear sealers are penetrating systems, whereas deck coatings are surface sealers.

Unlike clear sealers for vertical applications, the chemical composition of horizontal deck sealers is limited. It includes silicone derivatives of siloxanes and silanes and clear urethane derivatives. The majority of products are siloxane-based.

A sodium silicate type of penetrating sealer is available. This material reacts with the free calcium salts in concrete, bonding chemically to form a dense surface. The product is typically used as a floor hardener, not as a sealer. Sodium silicates do not have properties that sufficiently repel water and the chlorides necessary for protecting concrete exposed to weathering and wear.

To ensure sealer effectiveness to repel water, test results such as ASTM C-642, C-67, or C-140 should be reviewed. Reduction of water absorption after treatment should be over 90 percent and preferably over 95 percent. Additionally, most sealers are tested for resistance to chlorides to protect reinforcing steel and structural integrity of concrete. Tests for chloride absorption include AASHTO 259 and NCHRP 244. Effective sealers will result in reductions of 90 percent or greater.

Penetration depth is an important consideration for effective repellency and concrete substrate protection. As with vertical sealers, silanes with smaller molecular structure penetrate deepest, up to 1 /2 in. Siloxanes penetrate to a depth of approximately  1/ 4 – 3/ 8 in.

Urethanes, containing higher solids content, penetrate substrates approximately  1/ 8 in.

Silicone derivative sealers react with concrete and atmospheric humidity to form a chemical reaction bonding the material to a substrate. This provides the required water repellency.

Substrates can be slightly damp but not saturated for effective sealer penetration. Over dense, finished concrete, such as steel-troweled surfaces, acid etching may be required.

Since sealers are not completely effective against water-head pressures and do not bridge cracks, proper detailing for crack control, thermal and differential movement, and detailing into other envelope components must be completed. Expansion joints, flashings, and counterflashings should be installed to provide a watertight transition between various building envelope components and deck sealers.

Clear deck sealers are often chosen for application on balconies and walkways above  grade (not over occupied spaces) as well as for parking garage decks. In the latter, the upper deck or lower decks, which cover occupied areas, are sealed with deck coatings, while intermediate decks are sealed with clear sealers. (See Table 3.22.)

With certain designs, horizontal above-grade decks require the same waterproofing protection as below-grade areas subjected to water table conditions. At these areas, membranes are chosen in much the same way as below-grade applications. These installations require a protection layer, since these materials cannot be subjected to traffic wear or direct expo- sure to the elements. As such, a concrete topping slab is installed over the membrane, sandwiching the membrane between two layers of concrete; hence the name sandwich-slab membrane. Figure 3.51 details a typical sandwich-slab membrane.

FIGURE 3.51 Typical sandwich-slab membrane detailing. (Courtesy of TC MiraDRI)

In addition to concrete layers, other forms of protection are used, including wood decking, concrete pavers (Fig. 3.52), natural stone pavers (Fig. 3.53), and brick pavers (3.54). Protected membranes are chosen for areas subjected to wear that deck coatings are not able to withstand, for areas of excessive movement, and to prevent the need for excess maintenance. Although they cost more initially due to the protection layer and other detailing required, sandwich membranes do not require the in-place maintenance of deck coatings or sealers.

FIGURE 3.52 Protected membrane application using concrete pavers. (Courtesy of American Hydrotech)

FIGURE 3.53 Protected membrane application using stone pavers. (Courtesy of TC MiraDRI)

FIGURE 3.55 Insulation layer in protected membrane application. (Courtesy of American Hydrotech)

Protected membranes allow for installation of insulation over waterproof membranes and beneath the topping layer (Fig. 3.55). This allows occupied areas beneath a deck to be insulated for environmental control. All below-grade waterproofing systems, with the exception of hydros clay and vapor barriers, are used for protected membranes above grade. These include cementitious, fluid-applied, and sheet-good systems, both adhering and loose-laid. Additionally, hydros clay systems have been manufactured attached tosheet-good membranes, applicable for use as protected membrane installations.

FIGURE 3.55 Insulation layer in protected membrane application. (Courtesy of American Hydrotech)