Abstract: A substrate is coated with a coating composition (1) mainly composed of 3 to 16 parts by weight (in terms of an SiO.sub.2 basis) of a quaternary ammonium silicate (a), 15 to 85 parts by weight of an inorganic filler (b) and 12 to 82 parts by weight of water (c) (with the proviso that (a)+(b)+(c)=100 parts by weight), further with a coating composition (2) mainly composed of 2 to 15 parts by weight (in terms of SiO.sub.2) of a quaternary ammonium silicate (a)' and 98 to 85 parts by weight of water (c)' (with the proviso that (a)'+(c)'=100 parts by weight) as required, followed by hardening by drying at an ordinary temperature or by heat drying at a low temperature, thereby obtaining a noncombustible, weatherproof film.