PURPOSE: To repair a damaged part of lining easily in an extremely short time by making an opening for inserting the lance of a blowing repairing unit in the wall facing the damaged part composed of an iron skin and a lining, inserting a lance through the opening into a ceramic furnace and spraying refractory powder.

CONSTITUTION: An opening 11 of about 60 cm diameter is made through the wall of a mixing room facing the damaged part of lining under high temperature state (700-900°C) upon starting air supply while taking account of the position and the extent of damage. A lance 9 of a spray repairing unit is inserted through the opening and refractory powder is sprayed from a burner 10 at the forward end thereof to a damaged part C. After the damaged part is repaired, the opening 11 is closed to complete repairing work of a hot air furnace.