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Durable Waterprooﬁ ng
for Concrete Masonry Walls:
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
6/13/14 11:06 AM