PURPOSE: To manufacture a fiberboard of fixed quality free of dispersion.

CONSTITUTION: A calcium hydrosilicate bound fiberboard, in particular a double- deck board, is manufactured in a process wherein a fiber-binder-filler mixture having a 40 to 45 wt.% water content and a 55 to 60 wt.% solid content is prepared by digesting cellulose fibers equal to 2 to 12 wt.% of the solid content with water and mixing them with a filler and/or binder comprising cement and/or lime hydrate and substances containing reactive calcium silicates to form a thick pasty mixture. Then the thick pasty mixture of a predetermined amount is introduced into the frame of a bottom mold of a press consisting of top and bottom molds, almost completely leveled out, formed by closing the top and bottom molds, and dewatered through dewatering fabrics and channels in the top and bottom molds. Finally the mixture is compacted and vented, whereupon the molded raw board is demolded and autoclaved.