Abstract: An article is cast from a composition comprising a binding agent containing, by weight, from 90% to 10% calcined gypsum and from 10% to 90% Portland cement mixed with water to produce a fluid mixture which is caused to flow into a mould or other supporting device and is there allowed to set. To increase the durability of the cast article in the presence of moisture, sodium carbonate in an amount up to 5% by weight of the dry weight of the cement is added to the composition. The sodium carbonate is preferably present in an amount between 0.1% and 0.5% of the dry weight of the cement and the composition preferably also contains an acrylic resin emulsion in an amount from 0.25% to 4% of the dry weight of the gypsum and cement in the composition and a pigment such as iron oxide, titanium oxide or cobalt oxide in an amount from 0.25% to 4% by weight of the dry weight of the gypsum and cement in the composition.

Abstract: A method of making a cast article from a composition which contains a hydraulic binding agent comprising by weight from 90% to 10% calcined gypsum and from 10% to 90% Portland cement comprises mixing the composition with water to produce a fluid mixture, either the water or some at least of the components of the composition or both being heated so that the mixture has a temperature of from 70.degree. to 130.degree. F, and pouring the fluid mixture into a mould or other supporting device where the reaction of the calcined gypsum with the water causes the mixture to set and the heat of this reaction causes the temperature of the mixture to begin to rise. As soon as the mixture has set sufficiently to be self supporting, the set mixture, which forms the cast article, is removed from the mould or other supporting device and then the dissipation of both heat and moisture from the cast article is controlled so that the temperature of the article continues to rise to from 90.degree. to 180.degree. F.

Abstract: Box-like units having at least one open side for use, for example, in the construction of prefabricated buildings are cast from a composition of gypsum and water optionally including other material such as Portland or Aluminous cement. The mixture is cast between an external mould defining the external faces of the unit and an internal core defining the internal faces of the unit and the core is formed from, or covered with, material which causes its faces which come into contact with the mixture to have a higher co-efficient of heat reflection than that of the faces of the external mould which come into contact with the mixture. The mixture is allowed to set and the external mould is removed, after which the mixture is allowed to harden further and during this hardening becomes heated by the exothermic reaction between the gypsum and the water to cause the hardened mixture to expand away from the core. This allows the core to be subsequently removed without it being necessary to make the core collapsible.