ASTM C1177Full Name ASTM C1177 – Standard Specification for Glass Mat Gypsum Substrate for Use as SheathingScope This specification covers glass mat gypsum substrate, which is designed to be used as an exterior substrate for a weather barrier.Keywords core; exterior substrate; fire-resistant classification; flexural strength; glass mat; glass mat gypsum substrate; gypsum; hardness; humidified deflection; nail pull resistance; noncombustible; sheathing; substrate; type X; water resistance; weather barrierResourcesASTM International Website: ASTM C1177 Need more info?