Abstract: Calcium silicate monohydrate (2CaO.sup.. SiO.sub.2.sup.. H.sub.2 O) can be produced in a coating which has been formed by a coating material containing silica sol alone or silica sol and other additives such as aggregate, viscosity increasing agent, etc. by subjecting the coating to a chemical treatment such as heat-treatment, ultra-violet ray irradiation treatment, etc. in the presence of water and a calcium compound which may be present either in the coating material, or in the treating liquid, or in an object to be coated. The film which contains the calcium silicate monohydrate produced by said chemical treatment has remarkably high hardness and is excellent in water-resistance, water-imperviousness, weather-resistance, and heat-resistance.

Abstract: The surface of an inorganic substrate comprising cement, concrete, gypsum or mixtures thereof is treated with a silicate solution or a silica sol comprising a monovalent alkali metal containing component, an ammonium containing component and a silica containing component at a molar ratio of 1:1.about. 10:4.about.5000 corresponding to M.sub.2 O:[R.sub.1 R.sub.2 R.sub.3 R.sub.4 N].sub.2 O: SiO.sub.2 wherein M is Li, K or Na; and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each represent a hydrocarbon group or an alkanol group. The underlying inorganic substrate thus has a modified surface layer thereon having a thickness of less than 50 mm, which functions to protect and prevent deterioration of the underlying surface of said inorganic substrate.