Gypsum Plaster
This information reflects our best understanding of product composition in 2023.
Gypsum plaster is a combination of calcium sulfate hemihydrate, a mineral aggregate, and and additives. This Common Product describes gypsum plaster that is mixed on-site with potable water and applied to interior laths or masonry plaster bases....
Gypsum plaster is a combination of calcium sulfate hemihydrate, a mineral aggregate, and and additives. This Common Product describes gypsum plaster that is mixed on-site with potable water and applied to interior laths or masonry plaster bases. Gypsum plastering typically requires one or two base coats when applied to a gypsum lath followed by a finish coat. This CP describes gypsum plaster containing the mineral aggregate perlite. Perlite provides fire resistance and is lighter in weight than other commonly used aggregates but lowers the plaster's compressive strength. Additional additives include accelerators such as potassium sulfate and lime, which is frequently added to reduce the rate at which gypsum cures by absorbing carbon dioxide. Standards related to this CP include ASTM C28, covering various gypsum plasters, and ASTM C35, which covers inorganic aggregates used in gypsum plaster such as perlite, sand, and vermiculite.