PURPOSE:To obtain a brick chip with the slaking resistance improved by sizing the waste of a magnesia-carbon brick for the converter into a specified grain size and dipping the sized waste in a suspension of amorphous silica in water in vacuum for a specified time. CONSTITUTION:The waste of a magnesia-carbon brick for the converter is sized to 5-60mm, and the sized brick chip is preferably degassed for about one hour, dipped in a suspension of amorphous silica in water in vacuum for at least several ten minutes, preferably for one hour, taken out and dried. Consequently, the chip is impregnated with silica to the inside, and the structure is not broken by slaking or the breaking is reduced. A magnesia castable contg. 5-30wt.% of such a chip is excellent in resistance to slaking and spalling, hence the frequency of spalling is drastically reduced when applied to the actual furnace, and the castable is highly durable.