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Ensuring Durability of Elastomeric Wall Coatings Strong recommendations for better standards By David H. Nicastro, PE, F.ASTM, and Patrick D. Gorman Photos courtesy Building Diagnostics Inc. DURABILITY OF EXTERIOR COATINGS IS USUALLY CONSIDERED AS A FUNCTION OF WEATHERING, BUT AN ELASTOMERIC WALL COATING (EWC) MAY FAIL LONG BEFORE ENVIRONMENTAL EXPOSURE CAN CAUSE DETERIORATION. AS THE NAME IMPLIES, THESE PRODUCTS ARE SELECTED FOR THEIR ABILITY TO STRETCH, ESPECIALLY OVER A CRACK IN THE SUBSTRATE. IF THE CRACK PROPAGATES THROUGH THE COATING, THE SYSTEM CAN FAIL DURING ITS FIRST YEAR OF SERVICE. Many exterior cladding materials are porous, such as brick masonry, stucco, precast concrete panels, and some types of stone. Water is allowed to percolate through these claddings in a typical ‘drainage wall’ design; the water is then collected inside the wall cavity on a water-resistive barrier (WRB) and drained out through weep systems. It is unusual to coat these cladding materials during original construction, except there appears to be a trend to specify an elastomeric finish on stucco—perhaps as a solution to another stucco trend, cracking. 1 Concrete masonry unit (CMU) walls are often constructed with an elastomeric coating because they are so porous and usually lack a drainage system. When water leaks occur because of breaches in the concealed WRB inside a wall system, it is common to apply an elastomeric coating as part of a ‘barrier’ remedy, with the intent of keeping water from penetrating through the building envelope’s outermost surface. The coating system may involve several coats and a primer. They are often integrated with remedial sealant installation or wet-sealing windows to complete the barrier. 22 the construction specifier | july 2013 CS_July2013.indd 22 6/14/13 8:26:56 AM