Abstract: Intumescent sheet material having a matrix whose predominant ingredient is an unfired kaolinitic clay comprising ball clay reinforced by inorganic vitreous fibre (for example, mineral wool) contains heat-expandable graphite as intumescent agent and up to 10 percent by weight of an organic binder. It is made by dewatering an aqueous suspension of the aforesaid ingredients in the form of a layer which includes cellulose fibre as web-forming agent.

Abstract: Process for the concentration of fibrous material in a mixture thereof with non-fibrous material, by subjecting an aqueous suspension of the mixture to centrifugal force in a hydrocylone to obtain an overflow enriched in fibre and an underflow of reduced fibre content, the aqueous suspension which is admitted to the hydrocylone being the fibre-enriched fraction which results from a preliminary classification in which an aqueous suspension of lower fibre:non-fibre ratio is submitted to flow under conditions which bring about settling out under ordinary gravitational force of material reduced in fibre content and formation of a fibre-enriched fraction above it.In the process, the underflow flow from the hydrocylone is incorporated in the aqueous suspension which is submitted to the preliminary classification.