A process, apparatus and material composition for forming a coherent refractory mass on a surface wherein one or more non-combustible materials are mixed with one or more metallic combustible powders and an oxidizer, igniting the mixture in a combustion chamber so that the combustible metallic particles react in an exothermic manner with the oxidizer and release sufficient heat to form a coherent mass of material under the action of the heat of combustion, and projecting this mass against the surface so that the mass adheres durably to the surface.