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How does a modified bitumen roofing system work?

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Quick Answer

A modified bitumen roofing system uses asphalt, which is a traditional waterproofing medium, modified with atatic polypropylene, synthetic rubber, styrene butadiene styrene or other agents that form a uniform matrix to enhance the physical properties of the asphalt. The most common bitumen modifiers are atactic polypropylene and styrene butadiene styrene.

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Atactic polypropylene is a thermoplastic polymer that forms a uniform matrix within the asphalt, which enhances the performance of bitumen. The uniform matrix increases bitumen’s UV resistance, flexibility at low temperatures and flow resistance at high temperatures. Bitumen sheets modified with atactic polypropylene are usually applied with a propane-fueled torch that softens the bitumen on the underside of the sheet. The bottom surface becomes a molten adhesive that flows on the substrate before cooling to form a waterproof adhesive bond.

Styrene butadiene styrene modifies the asphalt by creating a polymer network within the bitumen. It gives the bitumen rubber-like features and enhanced resistance to weathering and aging. Styrene butadiene styrene-modified bitumen sheets are set in hot mopping asphalt, torch-applied or adhered using cold-process adhesives.

Given that modified bitumen roofing systems either lack seams or have strong seams, leaks and breaks do not occur at these seams when expansion and contraction occurs. This roofing system is also attached directly to the top of a building, eliminating the need for excess weight above.

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