Process for manufacturing reinforced roofing membranes

A process of manufacturing a roofing membrane that is free of any organic mat, comprising the steps of:

• selecting a lightweight polyester fabric consisting essentially of an open grid of over-under construction in which fill yarns are held between pairs of machine direction yarns lying essentially one above the other, the fabric having no mechanical connection at cross-over points of the fill and machine direction yarns and comprising polyester yarns having about 30 to about 300 denier yarns in the machine direction, about 30 to bout 300 denier yarns in the fill direction and a yarn per inch count of about 3.times.3 to about 10.times.10;
• applying to the fabric an adhesive binder that is one of dissolved and dispersed in a liquid for application to the fabric so that the open grid fabric is held together by the adhesive alone, the adhesive binder being applied to the fabric in a sufficiently large amount to accumulate between the two yarns of each pair of machine direction yarns and to bind the machine direction yarns together and hold the fill yarns between the pairs of machine direction yarns securely in subsequent processing;
• selecting a high strength reinforcing fabric consisting essentially of a non-woven open grid of polyester having no mechanical connections at cross-over points in the grid;
• combining the high strength reinforcing fabric with the adhesively secured lightweight polyester fabric;
• and
• passing the combination of the adhesively secured lightweight polyester fabric and the high strength reinforcing fabric with a fiberglass mat adjacent to the high strength reinforcing fabric, and any additional reinforcements free of any organic mat, through bituminous material to form the roofing membrane.