A two-piece, flush-mounting box designed for installing plumbing elements consists of the flush-mounting box itself and a flange that may be fastened to the side walls of the flush-mounting box at a certain distance from its front. The pressurized gas acts, in the form of individual gas pressure pulses, directly on the applicator part to generate the pressure waves or shock waves. A coated substrate includes the composition for application to a metal substrate and a coating on the composition.