Most clay masonry walls built today are veneers over steel studs, wood studs, or concrete block. Water that penetrates the exterior masonry is handled by the cavity and flashing at the base of the wall. But what about walls that have a single wythe of concrete masonry units ù wonÆt these walls leak?

Single-wythe concrete masonry walls are more prone to leakage than cavity walls. Unless the exterior surface is protected, water will penetrate these walls. Also, since conventional masonry units are relatively porous, they will readily absorb water, which can then soak through the concrete masonry walls and appear on the interior face. For this reason, most single-wythe concrete masonry walls are either coated with an elastomeric coating system or covered with plaster or some other system that will stop water from penetrating. Clear water-repellent coatings may also be used, although these treatments have limitations because they cannot bridge cracks or large mortar separations and, as with most coatings, must be reapplied periodically.

Typically, I recommend that the concrete masonry units used in single-wythe walls be manufactured with an integral water repellent that does not change the appearance of the unit and does not degrade with time. Face-shell-bedded walls with integral-water-repellent admixtures in both the units and the mortar can function very similarly to cavity walls if properly designed and constructed. Water that penetrates the exterior face of the wall will not be readily absorbed, but rather will drain through the cores of the units, similar to water flowing in a cavity wall. In these walls, it is extremely important that flashing be properly detailed at all openings and at the base of the wall to direct any water that penetrates the concrete masonry back toward the exterior. As in a cavity wall, it is important that these flashing joints be well-sealed and continuous at the corners.