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Durable Waterproofi ng for Concrete Masonry Walls: Redundancy Required by Robert M. Chamra, EIT and Beth Anne Feero, EIT All images courtesy Building Diagnostics Inc. SINGLE-WYTHE CONCRETE MASONRY WALLS ARE POPULAR BECAUSE THEY ARE INEXPENSIVE TO CONSTRUCT, AND COMBINE STRUCTURAL SUPPORT AND CLADDING IN ONE SYSTEM. HOWEVER, THEY CAN BE ASSOCIATED WITH LEAKAGE WHEN THE WATERPROOFING DESIGN IS SIMPLISTIC. A SINGLE-WYTHE WALL CAN, AND SHOULD, HAVE MULTIPLE WATERPROOFING COMPONENTS. 1 Concrete masonry units (CMUs) are characteristically porous building materials. When manufactured in accordance with the industry standard, ASTM C90, Standard Specification for Load-bearing Concrete Masonry Units, commonly used lightweight CMUs absorb up to 17 percent of their weight in water. This porosity is due in part to their composition. The mix for the units contains the usual concrete components of water, cement, and aggregates, but that third component will be a smaller coarse aggregate (i.e. gravel) than cast-in-place concrete. The smaller aggregate decreases the workability of the mix if all other variables are held constant. In some cases, this decrease in workability is compensated by the addition of water to the mix. Similar to cast-in-place concrete, the higher the water-to-cement (w/c) ratio in the CMU mix, the higher the permeability of the units. However, even a good-quality mix will remain permeable (Figure 1). 34 the construction specifier | july 2014 CS_July_2014.indd 34 6/13/14 11:06 AM