ASTM C1325-21 PDF Download

ASTM C1325-21 is a standard specification that applies to non-asbestos fiber-mat reinforced cementitious backer units. These units are designed to be dimensionally stable and can be used as an unfinished substrate or as a substrate for decoration, such as natural stone or tile, in wet and dry areas. The standard covers two types of flat sheets, type A and type B, depending on their intended applications. Type A sheets are suitable for exterior applications or as an unfinished substrate for cladding materials, while type B sheets are intended for covered exterior applications or as an unfinished substrate in interior wet or dry areas.

The standard specifies that the fiber-mat reinforced cementitious backer units can be manufactured with or without pressure and cured under natural or accelerated conditions. Mechanical and physical properties of these units, including flexural strength, density, and modulus of elasticity, must meet the requirements prescribed in the standard. The properties are determined on an uncoated product, whenever practical.

It should be noted that this specification does not apply to other types of cementitious sheets, such as asbestos-cement flat sheets, non-asbestos fiber cement flat sheets for exterior applications, gypsum backing board, water-resistant gypsum backing board, glass mat gypsum backing board, particle boards, and discrete non-asbestos fiber cement interior substrate sheets. These specific types of sheets are covered by other ASTM standards.