A formulation containing polymer, resin and cement combined with aggregate can be used as a gunnable mix that is applied to a surface by being conveyed pneumatically in dry form to a nozzle, where water is added. Polymer in the gunnable mix enables it to adhere and bond to a surface, such as carbon brick, of a lining of a vessel used for the containment of molten metals. The formulation may be used, for example, to repair and protect blast furnace hearth linings.