A thermal insulation is formed by simultaneously spraying ceramic fibers and a binder at a surface to be covered. An aqueous binder is prepared prior to application to the fiber during the spraying operation. The binder includes an organic component which provides necessary wet and green adhesion to the substrate surface and wet and green cohesion to the newly formed lining prior to firing of the sprayed-on layer. The binder also includes an inorganic component which functions at and after exposure to a high temperature to secure the ceramic fibers to the substrate and to one another. Drying and firing of the layer develops strength in the inorganic binder. Known ceramic fibers such as alumina-silica amorphous fibers, alumina-silica-zirconia fibers, polycrystalline mullite fibers, alumina fibers, mineral fibers, or combinations thereof, and the like may be employed. The fiber may be precoated with the organic binder. Preparation of the binder, coating of the fibers with an organic binder component and spray formation of the ceramic fiber insulation are described.