PURPOSE: To eliminate the need for a skill technique for correcting the irregular surface of a backing, and to easily conduct the correction in a short time by covering the mixture of aggregate and/or light-weight aggregate and a moisture curable urethane resin with a moisture impermeable film.

CONSTITUTION: A moisture curable urethane resin is mixed with 100 pts.wt. aggregate or light-weight aggregate at the rate of 2-150 pts.wt.. The bag of a polyethylene film is filled with a mixture under a nitrogen atmosphere by a film, in which a metallic foil is laminated on the resin film of polyethylene, polypropylene, polyvinyl chloride, polyester, etc., or these resin films, and the mixture is sealed and covered through heat sealing. The polyethylene film is cut simply in conformity with the size of an irregular surface, and the mixture is cured quickly by spreading the cut polyethylene film on the position of the irregular surface. Accordingly, an exclusive skill technique is not required for correcting the irregular surface of a backing, and the irregular surface is corrected easily in a short time, thus allowing the expectation of the large reduction of cost.