What is commonly called “tar and gravel” roofing is technically described as “built up roof membranes” or simply BUR. This is very commonly used for commercial roofing in Aurora IL and has been for well over 100 years.
A tar and gravel roof is made by building up alternating plies of bitumen and reinforcement until the membrane is completed. The roof is built up to a certain specified ply thickness with four plies being perhaps the most common. In most cases the first ply is fastened directly to the support structure of the roof.
The reinforcing material, called fabric, is usually roof felt of sheets of plywood. Roof felt used for commercial roofing is either organic in nature or it can be reinforced with fiberglass matting. Roof felt is normally delivered to the job site in rolls 36 inches wide.
The bitumen that is used can be either asphalt or coal tar. Regardless of what is used it is heated in a kettle and then liberally applied over the surface of the plywood or felt using a mop, roller or a mechanical device that spreads the bitumen evenly. Asphalt is derived from petroleum as it is refined from crude oil. Coal tar on the other hand is distilled from coal. Although asphalt and coal tar are by far the most commonly used there are cold applied adhesives as well.
The top surface of the flat roof is normally aggregate; it can be pea gravel, slag or mineral granules. As an alternative the top layer can be reflective aluminum or an elastomeric material. A three ply BUM roof using a modified polymer bitumen membrane is a hybrid which is gaining in popularity.
This type of roofing was originally developed in Europe in the 1960s, in the early 70s the roofing system was exported to the United States where it quickly gained in popularity. Basically the roofing system consists of a reinforcing fabric, this acts as a carrier for the hot modified polymer bitumen which is factory applied. The finished membrane is then delivered in rolls to the job site. Those in the industry refer to this type of roofing system as “MB”, modified bitumen.
MB commercial roofing in Aurora IL is available in two different types:
* SBS which is installed with hot mopping of asphalt or cold adhesive although some membranes have an adhesive back which eliminates the need for hot asphalt or other adhesive method.
* APP modified polymer membranes which are applied with an open flame torch or welded. This type of membrane is not recommended where the roof deck is wood for obvious safety reasons.
APP modifiers give the finished roof a plastic quality whereas SBS have more of rubber quality asphalt. Another type of membrane that is often confused with MB is a thermo set membrane called EPDM, this type of roofing is normally called “rubber roofing”.
Visit Showalter Roofing to know more.
