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.