Abstract: The portable apparatus for cementing edges of lengths of sheet material in adherent relationship over a roof comprises a horizontally oriented base structure having contact means at its lower surface for applying pressure upon the sheet material. The base structure has one substantially straight lateral side which is located adjacent and parallel to an imaginary vertical plane. The apparatus includes a brush member for applying cementing fluid underneath an edge of sheet material. The bristles of the brush member are at an angle of between about 90.degree. and 140.degree. with respect to the main body of the ferrule in which the heel end of the bristles are retained. A ferrule holder holds the main body of the ferrule of the brush member in vertical orientation next to the aforenoted imaginary vertical plane at a location forwardly beyond the leading edge of the base structure, with the bristles of the brush member extending away from the imaginary vertical plane.