A. Ron Webber, owner of Prime Plastering in Irvine, Calif., responds: There are many available deck waterproofing systems, and they aren't all installed the same way, so check with the manufacturer for the correct installation technique. Generally speaking, most leaks occur at termination points, including the transitions between deck and wall metal, deck and door threshold, and deck and door jambs. Other trouble areas include the attachment point for handrails and the area around scuppers and drains.
All penetrations and terminations should be flashed in a weatherboard (overlapping) fashion, with a minimum horizontal overlap of 2 inches and a minimum vertical overlap of 6 inches. Deck-to-wall joints must be lapped and caulked or soldered.
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