Abstract: To reduce the impact velocity of the concrete mass upon a surface, such as a wall, a branch line is arranged at the concrete conveying hose and at a point removed from the spraying nozzle. The branch line is intended to carry compressed air and opens into the surroundings. This branch line has a valve for regulating the quantity of compressed air which is to be withdrawn. By means of the branch or withdrawal line there is appreciably reduced the rebound of the concrete mass at the wall. The concrete mixture is initially pre-moistened to a constant moisture content before it arrives along the spraying or injection path and at the spraying or injection nozzle there is added thereto a constant residual water quantity. This method affords a continuously constant water content and renders possible reduced pressure of the conveying air since the concrete mixture is only pre-moistened at the conveying path.