This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
Asbestos mortar consists of a mixture of asbestos with 10 per cent of white lime. Canadian asbestos is generally used, which is composed of 80 per cent of asbestos and 20 per cent of serpentine. The asbestos is ground and the coarse powder used for the first rough cast, while the finer material is employed for the second top-plastering. This mortar is highly fire-resisting and waterproof, is only half as heavy as cement mortar, and tough enough to admit of nails being driven in without breaking it.