Rainwater penetration through exterior masonry walls to the interior space is causing serious problems around the country, even in some new buildings. Most contemporary walls are designed and built as a cavity system with a masonry veneer (clay brick, concrete brick, stone, etc.), air space, and backup materials.

This wall arrangement is normally designed under the assumption that some moisture could penetrate the exterior cladding, but should not migrate through the recommended 2-inch clear air space located between the masonry veneer and backup system. Any moisture getting through the exterior cladding should migrate down within the air space and drain out from the wall system through the weep holes.