Process for manufacturing a waterproofing assembly of laminated bituminous roofing membranes

A process for manufacturing a built-up bituminous roofing or waterproofing assembly, utilizing a self-adhesive, multi-layer, laminated, bituminous roofing membrane, comprising a flexible base sheet having on at least a portion of one surface thereof a first surface coating layer of uniform thickness applied in direct face-to-face mutually adhering contact therewith, said first surface coating layer consisting essentially of a substantially solid, waterproofing roofing bitumen;

• a second surface coating layer of uniform thickness superposed on said first layer and having its inner surface in direct, face-to-face, mutually cohering contact with the outer surface of said first surface coating layer, said second coating layer being of lesser thickness than said first coating layer and consisting essentially of a compound bitumen containing from about 5 to 95 percent by weight of substance selected from the group consisting of rubber, thermoplastic resin and mixtures thereof, said compound bitumen being of high tackiness at ambient temperature and being self-adhesive to the compound bitumen layer of another like roofing membrane;
• and a release sheet having a release surface in direct face-to-face releasably adhering contact with the outer surface of said second coating layer, comprising the steps of
• a. laying a plurality of said roofing membranes over a substrate so that said membranes partially overlap,
• b. removing the release sheets from the roofing membranes to expose the second layers thereof,
• c. placing said second layers in direct face-to-face contact and pressing said second layers together to form a waterproof joint therebetween.