Monday, June 24, 2013


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).

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

Changes in envelope plane require detailing prior to elastomeric application.
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).

Large movement crack or joint repair for elastomeric coatings.
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).

Reemulsification of coating.
FIGURE 3.19 Reemulsification of coating.

Monday, June 17, 2013


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.


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.


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.


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).

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

Monday, June 10, 2013


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).

Spray application of cementitious membrane on negative side.
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,

Tuesday, June 4, 2013

CEMENTITIOUS COATINGS: Properties and Installations

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.

Spray application of cementitious waterproofing.
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.

Block cavity wall waterproofing using cementitious waterproofing.
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.

Typical detailing of tunnel waterproofing applicable to above-grade applica- tions.
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).

Waterproofing concrete block envelope with cementitious coating
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
 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.