A mineral finish, typically in the form of slate flakes or granules, plays a crucial role in the performance and durability of bituminous roofing membranes.
Benefits of a Mineral Finish:
1. Protection Against UV Radiation and Weathering
One of the primary functions of slate or granules is to shield the bituminous membrane from UV rays, ozone, acid rain, and extreme temperature variations. Without this protective layer, the bitumen deteriorates faster, leading to drying, cracking, and reduced lifespan of the roofing membrane.
2. Safe for Rainwater Harvesting
Mineral-finished membranes ensure cleaner rainwater when compared to exposed bituminous membranes. The mineral layer prevents the release of oily or volatile substances into the runoff, making the harvested water more suitable for reuse (e.g. garden irrigation or toilet flushing).
3. Improved Performance of PV Systems and Rooftop Equipment
A light-colored mineral finish (such as white or light grey) can help reduce surface temperatures on the roof. This directly benefits solar panels, which operate more efficiently at lower temperatures. Other rooftop installations, such as HVAC systems, also benefit from a more stable thermal environment.
4. Aesthetic Value
Mineral finishes are available in a variety of colors (grey, black, red, white, etc.), giving architects and building owners design flexibility. This allows the roof to match the aesthetic of the building or comply with local architectural or planning requirements.
Differences Between SBS and APP Membranes
APP Membranes (Atactic Polypropylene / Plastomeric Bitumen)
APP membranes are naturally more resistant to UV and aging, which means they can be installed with or without a mineral finish, depending on the roofing setup and application. This does not negatively affect their durability.
SBS Membranes (Styrene-Butadiene-Styrene / Elastomeric Bitumen)
When used as a top layer, SBS membranes are always finished with mineral granules. Although SBS bitumen is highly elastic, it is more vulnerable to UV radiation. A mineral finish is therefore essential to protect and extend the service life of the membrane.