To obtain a slag splash coating for protecting the surface of a lining refractory in the suitable slag composition and slag temp. by deciding the charging quantity of auxiliary material for reforming the slag based on the slag composition measured at the end stage of refining molten metal or melting the metal and charging this auxiliary material into a furnace during treating.

The auxiliary material is desirable to be mixture of one or more kinds among MgO, CaO, SiO2, Al2O3, lime, raw dolomite, light burnt dolomite, light burnt magnesia, dead burnt magnesia and decarburized slag. Coating of the slag onto the surface of the lining refractory is executed by blowing gas against the residual slag in the furnace to develop the slag splash, and the gas used for the slag splash is desirable to be one kind or two kinds of mixed gas among air, nitrogen and exhaust gas from a converter. In this way, the charged auxiliary material is sufficiently melted to form the good slag coating layer, and the unit requirement of the blown monolithic refractory is reduced and the service life is extended.