Gypsum is a hydrous calciu~ sulphate (CaS04.2HiO), which, when calcined at temperatures ranging from 250° to 400°F, releases three quarters of its chemically • combined water. The resulting hemihydrate of calcium sulphate, commonly referred to as plaster of paris, when mixed with water, can be moulded, shaped or spread and subsequently dried, or set, to form a hard plaster product. Gypsum is the main mineral constit• uent in gypsum wallboard, lath and tile. Anhydrite, the anhydrous calcium sulphate (CaS04), is c'ommunly associated geologically with gypsum.
Crude gypsum is crushed, pulverized and calcined
IO form stucco, which is mixed with water and agn:ga1e (sand, yemticulite or expanded perlite) and
applied over wood, metal or gypsum lath 10 form . interior wall finishes. Gypsum board, lath and sheath• ing are formed by introducing a slurry of stucco, water, foam. pulp and starch between two sheets of absorbent
paper, which results in a continuous "sandwich" of wet
board. As the stucco hardens, the board is cut to preJetermined lengths, dried, bundled and stacked for shipment.
Crude gypsum is also used in the munuiacture of
portland cement where it acts as a retarder, to control set. It is used as a filler in pa.ru and paper manufacture, as a substitute for saltcake in glass manufacture and as a soil conditioner.
Production of gypsum in Canada is closely related
to activity in the building construction industry, particularly to activity in the residential building sector, in both Canada and the eastern United States. About
75 per cent of Canadian gypsum production is exported
to the United States. It is not surprising, therefore, that as a direct result of the economic recession in the United St.ucs, which was harshly felt throughout the
constructio» industry. exports of crude gypsum from Canada were reduced in 1974 by 9.4 per cent. Most of the gypsum for export is quarried in Nova Scotia by Canadian subsidiaries of United States gypsum prod• ucts manufacturers. Although most of the output from other provinces is used rc,!i• .nally, nearly all of the Nova Scotia production i-, • exported in large "in• company" shipments to the eastern United Stares,
Total construction in Canada in 1974 is estimated to have reached a value of over $23 billion, 60 per cent of which is credited to the building construction sector. Traditionally, one half of building construction expen• ditures are in the residential catego.y where, in 1974,
housing starts were down by 17 per cent to 222,123 units. .
Production of gypsum wallboard, lath and sheath•
ing increased slightly in 1974. Plaster production
decreased by over 16,000 tons to 105,483 tons, reflecting the effects of work stoppages at a number of gypsum products plants. The problem of material shortages within the construction industry carried through mid-year as suupliers and contractors were evidently reluctant to enter agreements which could be seriously affected by inflationary pressures. A high level of uncertainty prevailed in the construction industry, marked by hesitant and cautious commit- men ts.

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