PURPOSE: To prevent tiles and mortar from peeling off by pressing a mold material in which multiple projections are formed against placed concrete surface of which strength reaches at a specified limit for stamping.

CONSTITUTION: A material with good peeling-off property from concrete such as, for example, synthetic resin, etc., is formed in sheet shape, its plate thickness is determined properly to give a specified strength, and multiple protruded parts 2... are formed at specified intervals to provide a molding material 1. In the protruded part 2, a conical recess 2a is formed so that it is projected to the application surface side, its top is recessed to the opposite side to form a top surface bent part 2b, and both of them are formed integrally. When placed concrete strength reaches a specified limit, the mold material 1 is pressed against placed surface to form multiple recesses in the concrete surface by the projected part 2 of the mold material 1.