Masonry Magazine October 2006 Page. 40
DRAINAGE
inside of the inner wall (block back-up wall or sheathing in a veneer) on which moisture can flow unobstructed to the bottom. Whether this is primarily an air barrier, vapor barrier or weather barrier is debatable. The moisture must be able to follow the path to the bottom of the wall. All of this, however, is a moot point if proper flashing is not installed.
Stone, Manufactured Stone and Thin Stone
Stone, manufactured stone and thin stone all have their own moisture issues too. The same principles apply to solving these potential problems.
Stone should have a cavity behind it in order to prevent moisture from getting to the inner wall. I've seen instances where stone is fully grouted to an above-grade, wood frame structure - this is a sure way to create mold and to have permanent moisture problems. Stone walls should have a cavity wall design and mechanical ties to the inner wall; also, the cavity should be clean.
Thin stone and manufactured stone both let moisture through and have a significant quantity of mortar joints for even greater moisture intrusion. Neither system usually provides an opportunity for a typical one-inch minimum cavity. One solution in this application is to install a full-wall rain screen behind the scratch coat and expanded metal lathe. Once again, the minimum rain screen thickness should be sufficient to allow for convection drying of the inner wall and the system must have a weather, vapor or air barrier plane for moisture to drain to the bottom of the cavity. Weep holes are also an essential element in this application.
Ultimately mortar buildups between the masonry wall and the inner wall are, in themselves, not the problems, but rather the poor ventilation and drainage they create. By installing a masonry drainage device that allows for proper drainage and ventilation, despite the presence of mortar buildup, we can eliminate the damage without the costly and time-consuming techniques of trying to eliminate mortar buildup.
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38 Masonry
October 2006
CIRCLE 214 ON READER SERVICE CARD
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