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.

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