There are three stucco wall systems in use today: traditional three-coat stucco, so-called one-coat or synthetic stucco systems, and EIFS (Exterior Insulating Finish Systems). While water damage in EIFS walls has made the news in recent years because of class-action lawsuits, the fact is water can and does penetrate the finish in all three systems. This is especially true in houses with little or no roof overhang, where excessive amounts of water can run down the wall. The solution to building a water-tight stucco wall is to view it as a system in which all parts must be correctly installed, particularly at penetrations, joints, openings, and other areas susceptible to leaks. Too often, however, the stucco finish gets all the attention, while the underlying protective membranes and flashings -- which are the main defense against water intrusion -- are overlooked. In my 24 years as a stucco contractor, I have gone beyond the minimum requirements of the code to devise flashing details that have withstood the test of time. In this article, I will explain the materials and techniques I use to prevent leaks in stucco walls. In every case, you can tell if you have installed the flashing and building papers correctly by imagining the path water will take if you were to spray the wall with a hose before applying the plaster. If the water can flow freely over the paper from layer to layer without ponding or finding its way inside, then the wall is properly flashed.

I work primarily with one-coat and traditional stucco, both of which rely on water-resistant membranes in conjunction with flashing at all wall openings and penetrations to direct any water that makes it through the stucco down towards the bottom of the wall. EIFS systems, which are applied directly over foam, originally relied on a water-tight...

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