TL-0009 — Fastener Sealability Technical Letter (US Version)
GCP’s self-adhered underlayments (GRACE ICE & WATER SHIELD®, GRACE ICE & WATER SHIELD® HT, GRACE ULTRA™, GRACE SELECT™, Roof Detail Membrane™ and GCP granular underlayment ) are formulated to provide a quality seal around fastener penetrations. However, the quality of that seal can be significantly affected by the type of fastener used and the manner in which they are installed.
For best results, use smooth shank electroplated galvanized fasteners. Hand nailing generally provides a better seal than power activated nailing. Do not install the fasteners through the underlayment over unsupported areas of the structural deck, such as over the joints between adjacent structural panels. In addition, the fasteners should be installed as straight as possible so the membrane is not torn. It is important that the temperature at the time the fasteners are installed through membrane is 40°F (5°C) or higher for optimum sealability. If fasteners are removed leaving holes in the underlayment, the membrane must be patched with a round piece of membrane extending past the damaged area 6 inches (150 mm) in all directions. Underlayments may not self-seal open fastener penetrations.
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Last Updated: 2021-02-05