Abstract: An apparatus for sealing the lap joint formed by the edge of an upper sheet of roofing material overlying the edge of a lower sheet comprises a frame, a handle assembly mounted to the frame, a drive assembly including an endless belt which contacts the roof and is wrapped around a pair of spaced rollers mounted for rotation to the frame, a solvent delivery assembly mounted to the frame for applying solvent material between the overlapping edges of the roofing sheets, and a plurality of spring-biased casters mounted to the frame and extending downwardly into contact with the endless belt. The spring-biased casters are adapted to urge the belt against the upper roofing sheet and into contact with the lower sheet, thereby permitting the solvent material to create a bond therebetween. The spring-biased casters are arranged in an array so that pressure is applied to the entire lower run of the belt which contacts the roof surface.