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.

1.1 This specification covers non-asbestos fiber-mat reinforced cementitious backer units manufactured to be dimensionally stable and suitable as either an unfinished substrate (see Note 1) or as a substrate for decoration such as natural stone or tile on walls, floors, or decks in wet and dry areas. It is also suitable to be used as a substrate in the Application of Class PB Exterior Insulation Finish Systems (Practice C 1397), the Application of Direct-Applied Finish Systems (Practice C 1516), and the Application of Exterior Insulation Finish Systems Class PI (Practice C 1535).

Note 1—When used as an unfinished substrate, consult the manufacturer's written installation literature for proper application details.

1.2 This specification is not applicable to asbestos-cement flat sheets (Specification C 220); non-asbestos fiber cement flat sheets for exterior applications such as claddings, facades, curtain walls, and soffits (Specification C 1186); gypsum backing board, coreboard, and shaftliner (Specification C 442); water-resistant gypsum backing board (Specification C 630); glass mat gypsum backing board (Specification C 1178); particle boards (Definitions D 1554); and discrete non-asbestos fiber cement interior substrate sheets (Specification C 1288).

1.3 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.