Abstract: A method of controlling the ratio of hydration time (HT) to open time (OT) in the manufacture of composite materials from a mixture containing hydratable calcium sulphate such as gypsum binders, aggregates, fibers, water additives and other additives is disclosed. The method includes adding a retarder-accelerator combination such as Retardan and potassium sulphate to the mixture and applying pressure. The retarder-accelerator combination and application of pressure provide advantageous reduction in the ratio HT:OT. More particularly, HT:OT can be reduced to less than 1.

Abstract: A process for producing fibrous composite materials from feed stock formed reliminarily from a gypsum binder and chopped cellulose fibers, and saturating the mixture with water to the extent of at least 1.2 times its normal hydrated state, and beating the material to provide a fleece that is then spread on a flat surface and subjected to pressure for a sufficient length of time to drive out a substantial portion of the moisture from the product. The compression step is carried out long enough to achieve a bulk density of approximately 9/10 the dry bulk density of the components prior to hydration.