Various types of sheathing boards, especially gypsum-based products, are the most common substrates for EIFS in North America. One question that frequently arises about substrates is, “How do I fasten them to the supporting framing?” Contrary to the all-too-common practice, attaching gypsum-based sheathing is not simply a matter of using the same fastener spacings as for interior drywall. There’s much more involved, and this article will give you some ideas about how to properly attach gypsum-based sheathings for use with EIFS.
Gypsum-based sheathings, like drywall, are a three-layer material. They consist of an outer facing, an inner core, and an inner facing. The facings are needed to give the boards strength against cracking due to bending. They also provide the gypsum-based core with some protection from water when on the wall prior to the application of the EIFS. Both paper and glass fibers are used for facings. Since neither the core nor the facings of gypsum-based sheathings are sufficiently strong to directly accept mechanical anchors such as screws or nails, attaching an EIFS to gypsum-based sheathings must involve either adhesives that bond the EIFS insulation to the sheathing, or mechanical fasteners that go through the sheathing into a structural material such as the studs, or both.