Prefabricated heat activated composite waterproofing membrane, composed of distilled bitumen and special synthesis polymers, which provide thermal adhesion properties to the lower face waterproofing compound. The waterproofing compound of the upper face allows for fast heat transmission to the lower face. The heat activated waterproofing compound allows the product to be positioned and applied without the initial use of heat. GRID BIT T.A. VIADUCTS is specifically developed for use on bridges, viaducts, parking decks and for all those applications where the use of road asphalt is required. GRID BIT T.A. VIADUCTS has a rot proof composite woven non woven continuous single strand heavy weight polyester with very high mechanical characteristics. The upper face is self protected with a woven non woven polypropylene mat. The lower face is provided with a thermoplastic removable film.