ASTM International Standard Specification for Fiber-Mat Reinforced Cementitious Backer Units ASTM C1325-21

This specification covers non-asbestos fiber-mat reinforced cementitious backer units manufactured to be dimensionally stable and suitable as either an unfinished substrate or as a substrate for decoration such as natural stone or tile on walls, floors, or decks in wet and dry areas. Flat sheets covered by this specification are divided into two types, according to their intended application: type A - sheets are intended for exterior applications as a substrate for other cladding materials, or as an unfinished substrate for decoration such as natural stone, tile, or coatings, and type B - Sheets are intended for covered exterior applications such as soffit areas, or for interior dry or wet area applications as a desired unfinished substrate or an unfinished substrate for decoration such as natural stone or tile, where substrate dimensional stability is required. These products are formed either with or without pressure and cured, either under natural or accelerated conditions, to meet the property requirements. Mechanical and physical properties shall be determined on an uncoated product wherever practical. The flexural strength, density value, and modulus of elasticity value shall be tested to meet the requirements prescribed.