A building material containing inorganic fibers (e.g. concrete containing asbestos or rock wool) is impregnated (by coating, spraying, dipping or pumping through injected needles (2, Fig. 3) with an aqueous solution of polyvinyl alcohol preferably of polymerization degree 250-500, or of such alcohol which has been denatured with an acid (e.g. maleic or sulfonic) and preferably of polymerization degree 500 or less, in amounts of 2-30 parts by wt. of PVA per 100 of water. Additives may be present in the solution, e.g. pigment or antiseptic.
The denatured PVA solution is a novel treating agent.
The solution used has excellent penetrating and film-forming properties and serves to adhere the inroganic fibers to prevent them from being scattered during building or demolition work.