A building board comprises a core 31 of set cementitious material, such as gypsum, faced on at least one side by a fabric or web 33 of mineral fibres embedded in the face of the core and a continuous film 32 of the cementitious material having a higher density and lower porosity than the core extending over the outer face of the fabric. The film may have a smooth surface or a desired textured or figured surface. The preferred fabric or web 33 is a non-woven glass fibre tissue and it is preferred that a continuous film 32 of gypsum at the surface should not exceed 2 mm in thickness. The board is made by bringing the fabric or web into contact with the respective face of a layer of an aqueous slurry of gypsum plaster or other cementitious material, and vibrating the layer of slurry in contact with the fabric or web until slurry penetrates the web and the latter is completely embedded. The process can be carried out continuously by supporting the slurry between flexible belts which are vibrated by mechanical action applied to their faces remote from the slurry. Boards accordingly to the invenion can have greater strength and/or greater resistance to fire than conventional paper-faced gypsum board.
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