Source: MASONRY CONSTRUCTION MAGAZINE
Publication date: December 1, 1998
- Are flashing systems required in ungrouted concrete masonry walls that have integral admixtures to prevent water penetration?
Flashing should be used in ungrouted masonry wall systems that have integral admixtures. Some water will penetrate the outer portions of virtually all masonry walls. Water also can enter through building joints, such as door and window openings, through roof leaks and in other ways. Concrete masonry walls without integral water repellents absorb considerable moisture. To work effectively, these systems must function as a surface barrier--a membrane or other treatment of the block's exterior surface--to prevent water penetration. Any water that penetrates this skin can be absorbed through the block or enter the interior, causing leakage. Flashing is less effective in these systems because, once water penetrates the outer skin, it can cause problems in the interior above the flashing, as the water wicks through the wall.Concrete masonry wall systems with integral admixtures will not generally have the same wicking problem as conventional concrete masonry. Water that bypasses the surface of these masonry walls typically flows down through the concrete masonry units' cores. Thus, flashing at the wall bases and above any openings, such as windows or vents within the masonry walls, serves as a second line of defense against water penetration. In this way, an ungrouted concrete masonry wall with an integral water repellent can function like a cavity wall. Just like wall systems with flashing, the wall must be designed to account for structural-strength loss where this flashing interrupts the bond within the wall. If flashing is not provided, the system must function as a surface barrier wall.
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