PURPOSE: To prevent furnace wall brick and iron shell from breakage caused by heat expansion at the time of refiring by pouring shrinkable mortar at inner circumferential part of side wall in furnace bottom after reducing height blowing down in a blast furnace and filling up the mortar into gap, etc., between solidified remaining iron slag and the side wall brick at the furnace bottom.

CONSTITUTION: At the time of executing reducing height blowing down, repair of furnace top part and refiring, the shrinkable mortar 10 is poured along inner circumference of the side wall brick 5 at the furnace bottom over all around the furnace after reducing height blowing down. Then, material containing the prescribed quantity of Al(OH)3 is suitable as this mortar 10. By this method, the mortar 10 is penetrated into coke packing layer 12 and the gap 4 between the solidified remaining iron slag 3 and the side wall brick 3 at the furnace bottom is filled up and also joint 5-1 of the side wall brick is penetrated and the gap 4 and the joint 5-1 are perfectly filled up and invasion of the foreign material is prevented. By this method, at the time of executing the refiring, even if the solidified remaining iron slag 3 heat-expands, as the mortar 10 is absorbed and relaxed, the breakage of the furnace wall brick 5 and the iron shell 6 at furnace bottom are not developed.