APP Modified

Final view of APP projectModified Bitumen (MB) is asphalt that has had modifiers added to it to give it plastic or rubber-like properties. The most common types of modifiers being used are APP (Atactic Polypropylene) and SBS (Styrene Butadiene Styrene). Rolls of modified bitumen membrane come in widths of 36" (0.9 m) to approximately 39" (1 m) and cover an area of approximately 100 square feet to 112 square feet per roll. Surfacings for these roll materials consist of a smooth surface, or mineral granules, aluminum, copper, or an aggregate such as gravel or slag that is set it hot asphalt.

Modified Bitumen roof systems consist of one, two, or three ply systems. The type of substrate will often determine the type of system being installed. Modified membranes can also be installed in conjunction with built-up roof materials (such as multiple plies of fiberglass felt) to form a "hybrid" roof system. Modifieds have proven performance on residential, commercial, and industrial applications.

Roofhelp recommends that all modified roofs be installed on slopes not less than 1/4" per horizontal foot (stated "quarter in twelve" or "quarter-inch slope") in order to achieve positive drainage.

Before and after APP

APP Modified Roofing Systems

APP installation projectIn order to create roofing grade asphalt, asphalt flux is air-blown at elevated temperatures which converts the flux to roofing grade asphalt. In the early 1970’s, the Italians, lacking the blowing equipment, were looking for a product that would convert asphalt flux into a usable roofing product. They discovered that if Atactic Polypropylene (APP) - a by-product of propylene polymerization - was added to asphalt then it gave the asphalt some plastic properties. They found that by adding about 30% of APP modifier, they could stretch the modified asphalt up to fifty percent of its original length before it would break.

Next came the need to make it into a usable roll product. Some type of reinforcement would be needed. They looked into various reinforcement materials and decided on a polyester mat because polyester would accommodate the APP modified asphalt’s elongation properties whereas the more commonly used woven glass mats would not. The reinforcement material is dipped into the hot modified bitumen mix, then goes through a rolling cylinder, cooled, and then wound into a roll.

APP membranes are applied using a torch. The back of the sheet has extra asphalt on it which, when heated, bonds to the substrate. This was especially convenient for the smaller, more cut up roofs because less room and equipment is needed on site to torch-apply a membrane than is necessary for application using hot bitumen.

Contact APP modified bitumen roof installation specialists at Roofed Right for a quote.
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