INORGANIC CONSTRUCTIONAL BOARD AND METHOD OF MANUFACTURING THE SAME

An inorganic constructional board for use as a wall backing material comprises a middle layer portion formed mainly of inorganic foamed material with an adequate quantity of fibrous material and binder added thereto, and outer layer portions placed on both surfaces of the middle layer portion. Each outer layer portion is formed mainly of mineral fiber material and inorganic powder material with binder added thereto. The middle layer portion has a specific gravity of less than 0.4, and the outer layer portions each have a specific gravity of more than 0.7. The board is more lightweight than plaster board and has performance characteristics equivalent to or better than those of the plaster board. The board is manufactured by forming a wet inorganic mat constituting the lower layer portion, forming a middle layer portion on the lower layer portion, according to a dry process or a wet process, stacking on the middle layer portion a wet inorganic mat which constitutes the upper layer portion, pressing the stacked structure to form an integral laminate and heating the same to dry it.