Gypsum is a mineral consisting of water-containing calcium sulphate (CaSO4.2H2O). When calcined (roasted) at temperatures of 120-250°C, gypsum releases 75% of its water. The resulting plaster of Paris, when mixed with water, can be molded, shaped or spread, then dried or set to form hard plaster. Gypsum was used by the builders of the pyramids as a construction material and earlier by artisans producing decorative objects. Nova Scotia gypsum was shipped to the eastern US in the 1780s for use as land plaster. The popularity of gypsum as a building material grew from the mid-1880s as methods of controlling setting time were developed.

The principal use for gypsum is wallboard. Crude gypsum is pulverized and heated to form stucco, which is mixed with water and aggregate (sand, vermiculite or expanded perlite) and applied over wood, metal or gypsum lath to form interior wall finishes. Gypsum board, lath and sheathing are formed by introducing a slurry of stucco, water, foam, pulp and starch between 2 unwinding rolls of absorbent paper, resulting in a continuous sandwich of wet board. Gypsum is also used as a filler in paint and paper manufacture, as a substitute for salt cake in glass manufacture and as a soil conditioner.

Approximately 75% of Canadian production comes from Nova Scotia; Ontario, Manitoba and BC also produce gypsum. Wallboard manufacturers are located in these provinces as well as in Québec, Newfoundland, New Brunswick and Alberta. Crude gypsum is a low-cost, high-bulk mineral commodity. The US is the world's leading producer of gypsum, and other important producers are China, Iran, Thailand and Spain.

The present structure of the gypsum industry in Canada is expected to remain about the same, although future availability of synthetic gypsum resulting from more strenuous environmental controls will substitute for natural gypsum in some regions. The RECYCLING of scrap and waste gypsum from construction sites and wallboard manufacturing lines will continue to become more important in both Canada and the US.