APP (atactic polypropylene) and SBS (styrene-butadiene-styrene) are the two polymer additives that create the “modified bitumen”. Each has its own unique features, but both serve the same purpose; to dramatically enhance the weathering capabilities of the waterproofing asphalt.
The modified asphalts are combined with polyester or glass fiber to reinforce the membrane, providing high tensile strength and flexibility, maintained even in the coldest winter months. A great advantage to the use of APP Modified Bitumen is capability of direct heat-welding application. Sometimes referred to as “torch-down” or “roll roofing”, the rolls of material (36” x 33’) are applied using propane torches. This use is common in the installation of a two-layer modified bitumen system. The system involves a base layer of smooth, APP modified with a granular surfaced cap sheet heat welded to the base layer, providing a membrane mass of 315 mils. You can reasonably expect to get 25-30 years from this type of multi-layered modified bitumen replacement system.