SBS Modified Bitumen

SBS modified bitumen is roofing membrane made from asphalt blended with styrene-butadiene-styrene, a thermoplastic elastomer that gives the compound rubber-like stretch and recovery. It was developed in France and Germany in the 1960s with colder climates in mind, because it stays flexible at low temperatures.

Composition

A typical SBS compound contains about 10-15% SBS polymer, asphalt, and limestone or similar mineral filler (around 15%), sometimes with oxidation inhibitors. It is blended hot, around 175-200 C (350-390 F), for several hours. In tests reported by industry, SBS bitumen with about 10% rubber could stretch to several times its length and recover. The compound is coated onto polyester, glass-fibre or combination reinforcement.

Installation

SBS is the most versatile of the modified bitumens. It can be:

• mopped into hot asphalt, like a built-up ply
• torch-applied
• set in cold adhesives (solvent-based or water-based)
• supplied as self-adhered sheets

This flexibility lets contractors choose methods that avoid open flames, which is increasingly important to insurers and building owners.

Systems

The usual assembly is a two-ply system: a smooth or sanded base sheet and a granule-surfaced cap sheet. Three-ply systems and hybrid systems with built-up felts are also used. SBS sheets are widely used as flashing membranes on BUR roofs, where they handle movement better than felt strip-ins.

Surfaces

Cap sheets come with coloured or white mineral granules, foil faces or factory coatings. Reflective cap sheets can meet North American cool-roof requirements.

Comparison with APP

SBS has better low-temperature flexibility and elasticity; APP is stiffer and more resistant to heat and UV and is almost always torched. Both originated in Europe and both are made worldwide.