Abstract: The method comprises applying on the surface of each of the parts a thin layer of a curable first mixture containing a first resin which cures slowly and is slightly exothermic and has a good adherence to said surfaces. A curable second mixture is then introduced in a space defined by the layers of the first mixture in the final position of the two parts. The second mixture contains a second resin which cures rapidly and is sufficiently exothermic to promote the curing of the first resin and normally has after curing a poor adherence to said surfaces but a good adherence to the first resin.

Abstract: A strong, expanded moulded panel or board, having a specific gravity between 0.2 and 0.8, is produced by heating dry urea formaldehyde resin containing 4% to 8% volatile materials in a mould at between 130.degree. and 160.degree. C under light restraining pressure between 30 and 300 psi which permits moderate expansion of the resin owing to the gasification of the volatile materials.

Abstract: Expanded urea formaldehyde products are moulded from urea formaldehyde resin solution, a catalyst such as formic acid and, optionally, a foaming agent, casting the mixture in an open-topped mould, partially drying and curing the resulting gel at 20.degree. C to 70.degree. C to produce a preform, and subsequently heat-treating the preform above 120.degree. C in a restraining mould and allowing it to expand therein.