Abstract: A machine for seam welding overlapping heat weldable lengths of covering, comprising a wheel-borne frame having a heating element suspended on one side designed for insertion between an underlying and an overlying length of covering. The machine has pressing means and driving wheels for compressive stress of the upper side of the overlying length of covering and for movement of the machine in the longitudinal direction of the overlapping seam or lap. To make possible wheel transport of the machine, with the heating element raised from the underlying surface, and to make possible an easier guiding of the heating element between the two lengths of covering in the lap, the machine has especially positioned transport wheels which in the welding position will be lifted clear of the underlying surface, but by tilting the machine can be brought into contact with the underlying surface, so that the machine can be wheeled by means of the transport wheels.