To impart functions of finish coating films for inner and outer walls and photocatalyst coating films by forming the finish coating films for the inner and outer walls having a contact angle with water within a specific range on the surfaces of base materials for buildings and forming coating films of a water-base photocatalyst coating material containing silicone as a leveling agent for the finish coating films for the inner and outer walls thereon.

The contact angle with the water is 30 to 120°. The base materials for buildings are asbestos slates, lightweight foamed concrete boards, etc., and the finish coating materials for the inner and outer walls are a synthetic resin emulsion base and acrylic rubber base, etc., and a photocatalyst coating material is coating materials prepared by dispersing titanium oxide particles and amorphous titanium oxide into water, etc. The amount of the silicone to be added to the photocatalyst coating material is preferably 0.003 to 1.5 water. If the amount is 0.03 to 1.0 wt.%, air bubbles exist particularly on the surfaces of the lightweight foamed concrete panels, etc., and the leveling adjustment to the surfaces of the base materials for building having ruggedness is possible. The water-base photocatalyst coating films consisting of two layers of a pretreatment coating film and the active photocatalyst coating film are preferably formed by applying a pretreatment coating material on the surface prior to the coating application of the active photocatalyst coating material.