Modified Bitumen Roofs
Modified 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. Surfacings for these roll materials consist of mineral granules, aluminum, copper, or an aggregate such as gravel or slag.
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 in order to achieve positive drainage.
In 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 1970s, 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 asphalts 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.
While APP was being looked into in southern Europe, northern Europe was experimenting with a different type of modifier called Styrene Butadiene Styrene (SBS). The French and Germans found that if they added 10%-15% of SBS rubber to asphalt, the asphalts characteristics changed to those of the rubber additive. They learned that they could stretch the SBS modified asphalt up to six times its original length and that, unlike the APP, it would return to its original size when allowed to relax.
There are a wide range of reinforcements used in SBS roofing materials. These include fiberglass or polyester mats and scrims, or combinations of both. The fiberglass mats range in weight from 1.0 to 2.5 pounds per 100 square feet or around 50 to 125 grams per square meter. Polyester reinforcements range in weight from 3.5 to 5.0 pounds per 100 square feet or 170 to 250 grams per square meter. The type of reinforcement used depends on the materials performance requirements.
SBS membranes can be hot asphalt applied, torch applied, or cold process applied.
COAL TAR MODIFIEDS
Information coming soon!
|Contents of this site copyright ©1998, 1999 RoofHelp.com. All rights reserved.|