1.1 This specification covers water-resistant gypsum backing board that is designed primarily to be used as a base for the application of ceramic or plastic tile on walls or ceilings. This product is also suitable for decoration.

Note 1-Specification C840 contains application procedures for water-resistant gypsum backing board.

1.2 The values stated in either inch-pound units or SI (metric) units are to be regarded seperately as the standard. Within the text, the SI units are shown in brackets. The values stated in each system shall be used independent of the other. Values from the two systems shall not be combined.

1.3 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.