This specification covers coated glass mat water-resistant gypsum backing panel designed for use on ceilings and walls in bath and shower areas as a base for the application of ceramic or plastic tile. Coated glass mat water-resistant gypsum backing panel shall consist of a noncombustible water-resistant gypsum core, surfaced with glass mat, partially or completely embedded in the core, and with a water-resistant coating on one surface. The specimens shall be tested for flexural strength, humidified deflection, core hardness, end hardness, edge hardness, nail pull resistance, water resistance, and surface water absorption. Coated glass mat water-resistant gypsum backing panel shall have surfaces true and free of imperfections that render the panel unfit for its designed use.