Abstract: Starting from a mark (G) provided on a wall of the room, plugs are cut from a plastic rod (11), which is adjustable within a tube (1) of the tool, which is supported through legs (3; 23) by the underground . The cutting takes place at the location of a quantity of adhesive provided on the ground, so that the plug adheres to the ground. The upper surfaces of the plugs then indicate the correct height of the floor of flowing mortar to be provided. The correct plug height is obtained at each location when a laser receiver (9; 35) connected to the tube is coincident with a stationary positioned laser beam (20).