Welding apparatus and method for joining roofing materials

1. Field of the Invention Pressure roller and heating element combination for a welding apparatus and a method designed to weld a first thermoplastic sheet laid on the deck of a roof structure and secured to the deck by a line of fastening means, and an overlapping second thermoplastic sheet disposed over the line of the fastening means. The pressure roller includes a distal end, a proximal end, and a center portion which defines a groove. The groove is provided with an elastomeric cushion to smoothly ride over the line of fastening means and expel air from between welds produced on both sides of the fastening means when the apparatus is advanced in tandem with a heating element longitudinally along the overlapping portions of the thermoplastic sheets.