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News / Past Articles


By Lee G Jones

Q    How do you determine whether glass mat gypsum substrate is still good after being exposed to the weather for some time before attaching EPS board for the installation of an exterior insulation and finish system? Can you do an "X test," similar to how you test regular gypsum sheathing? A    The "X test" that is used to check the condition of gypsum sheathing does not work for glass mat gypsum substrate. In fact, when I called a manufacturer's technical service department to pose the question, there was a long pause followed by some quick conferring, then a "Sure, you can try it, but we've never heard of anyone doing that before." When I pushed further, asking how then does one determine whether the material is still viable, I was told that to date this has not been a problem. Clearly, though, it is important to ensure that the substrate is in fact in a usable condition before attaching the many components of an EIF system, especially having been exposed to the elements for an indeterminate period. So, to follow up on this question, I called one of my gurus who told me that the best way he's found to evaluate the condition of a glass mat gypsum substrate is to find an edge that has been cut for an opening or penetration and check the condition of the core. If it's beyond its time, the core will be crumbly, in which case it should be replaced before continuing. Q    How do I find out what the correct pattern for installing mechanical fasteners is when attaching EPS board for an EIF system? Some say to stagger the fasteners, others say to keep them in straight rows. A    Naturally, getting the correct answer depends on a couple of factors. For starters the type of substrate will affect the recommended pattern: for instance, if the sheathing is a wood product (plywood or OSB), you can attach the fasteners right into the sheathing; however, if the sheathing is a gypsum product, you must find the framing member to properly install the fasteners. Then there's the thickness of the EPS, which may affect how tightly you must space the fasteners. According to ANSI/EIMA 99-A-2001: "Mechanical fasteners and washers shall be of a type and spacing in accordance with the EIFS manufacturer's current published instructions and shall be included in the project plans and specifications." So, if you're on the job and there's a copy of the contract documents handy, you might find the recommended fastener pattern spelled out in the specks, but if you know who the EIFS manufacturer is and what system is going to be used, you can probably download this information from the manufacture's Web site. Just by pulling up a couple of EIFS manufacturers' Web sites and typing in "mechanical attachment," I quickly had several different sets of patterns for mechanical attachment in a variety of situations. Q    Where should window head flashing be installed on a drainable EIF system? A    Now that many EIFS jobs are switching to "water managed" systems, there's usually some kind of weather-resistive barrier (house -wrap) that must be integrated with the flashings, and in some cases the necessary layering is counter-intuitive. The key thing to remember is that the flashing is normally designed to direct intruding water to the exterior surface of the wall, not to the drainage plane behind the EPS board. So, over a window, the flashing should be between the substrate/sheathing and the weather-resistive barrier, where moisture captured by the weather-resistive barrier will be directed via the flashing back outside where it belongs.

About the Author

Lee G Jones is AWCI's director of technical services. Send your questions to him in care of AWCI's Construction Dimensions , or send your e-mail question to jones@awci.org.     



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