Abstract: After newly attaching an interior-finishing vinyl wall covering onto at least one of a wall, floor and ceiling of a building, or after completion of washing/renovation of the vinyl wall covering, a liquid or slurry coating material containing a titanium oxide, a layered silicate mineral, and a silver ion and/or a copper ion, is sprayed or applied onto a surface of the vinyl wall covering. Subsequently the coating material is naturally dried to form a thin transparent coating layer. In a process of renovating the vinyl wall covering, the coating layer is removed by washing with water or wiping with water to completely remove various stains. The present invention makes it possible to allow any worker, i.e., even an unskilled worker, to fully renovate an interior-finishing material, such as a vinyl wall covering, without difficulty and at low cost.