FIELD: manufacture of building materials. SUBSTANCE: before applying impregnation composition (solution of at least one phosphate), composite product is subjected to treatment with aqueous solution penetrating inside opened internal pores of material and then dried. Aqueous solution contains additive imparting to dried composite product increased wettability for impregnation composition, said additive preferably being at least one water-soluble nonionic surfactant such as oxyethylenated fatty acid, oxyethylenated fatty alcohol, oxyethylenated alkylphenol, or higher polyatomic alcohol ester. EFFECT: increased oxidation protection efficiency in bulk of material. 7 cl, 5 dwg, 1 tbl, 5 ex
