Masonry Magazine December 2008 Page. 28
FLASHING AND DRAINAGE
"Excess mortar is held in proximity to the mortar joint and will push slightly into our masonry mat, but it won't be able to make contact with the back-up," Atkins says, "so, you still have an area where moisture can drain and air can ventilate."
The major method of water control within the cavity is the use of flashing. Flashing, at a minimum, must come through the wall to remove moisture that gets behind the outer wythe.
The technical notes of the Brick Industry Association (BIA) address flashing a masonry wall (www.bia.org/bia/technotes/t7a.pdf):
"Selection of a proper flashing material is of utmost importance, because the flashing is a critical element to the drainage of water that may penetrate the wall system. Flashing materials should be waterproof, durable and resist puncture and cracking during and after construction. Because flashing may be installed in advance of the exterior brick wythe, it should be able to endure some exposure to ultraviolet (UV) light without significant deterioration. The flashing should also resist damage from contact with metal, mortar or water and be compatible with adjacent adhesives and sealants. In general, thicker flashings are more durable, but may be more difficult to form.
Flashing materials generally fall into three categories: sheet metals, composite materials (combination flashings) and plastic or rubber compounds. The selection is largely determined by cost and suitability. It is suggested that only superior quality materials be selected, since replacement in the event of failure may be expensive. Materials such as polyethylene sheeting, asphalt-impregnated building felt, building paper and house wraps should not be used as flashing materials. These materials are easily damaged during installation and in many cases, turn brittle and decay over time."
Chris Bupp, head of the Educational and Architectural Services Division at Hohmann and Barnard in Hauppauge, N.Y., adds, "The recommendation has been that you should go beyond the face of the brick or the veneer material one-quarter of an inch to form a drip edge. The BIA has, in the few last years, revised that to say that, while that is still the recommendation, they now have
HOHMANN AND BARNARD, INC.
HB TEXTROFLASH™
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