GB540415A - Improvements in or relating to calcium sulphate plasters - Google Patents

Abstract

540,415. Synthetic resin compositions. LEFEBURE, V., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. April 8, 1940, No. 6297. [Class 2 (iii)] [Also in Group V] In the production of calcium sulphate plasters which are mixed with aqueous ureaaldehyde syrups immediately prior to use, setting of the plaster is accelerated by incorporating in the calcium sulphate not more than 2 per cent. of a salt which dissolves in water to give an acid reaction thus causing hardening of the resin. Salts specified are potassium and sodium hydrogen sulphates and alum. Ammonium hydrogen sulphate and ammonium chloride may also be used but have the disadvantage that ammonia is evolved by re-action with the lime. Retarders may also be added to prevent too rapid setting, e.g. fused meta- and pyro-phosphates as described in Specification 458,437, [Group V], or keratinous refuse and dry hydrated lime (up to 0.1 per cent.). A plaster is prepared by mixing 10 cwts. calcium sulphate hemihydrate plaster with 6 lbs. organic scutch retarder and 6.7 lbs. powdered potassium hydrogen sulphate and then adding a further 10 cwts, plaster with further mixing. For use 100 parts of the plaster are mixed with 12¢ parts urea-formaldehyde syrup containing 75.5 per cent. resin and 47¢ parts water. The mixture may be used for the core of plaster boards or as an adhesive for bonding layers of plaster board as described in Specifications 540,326, [Group VIII], and 491,882, or as a camouflage applied to hessian or canvas backings.