Silicone Roof Coating

Silicone roof coatings are elastomeric coatings based on silicone polymers. Most are moisture-curing, high-solids products that build film thickness quickly in one or two coats. Silicone's chemical structure makes it very resistant to ultraviolet light and weathering, so it ages more slowly than many organic coatings.

Uses

• restoration of single-ply, modified bitumen, BUR and metal roofs
• protective top coat for spray polyurethane foam roofs
• areas where some ponding cannot be eliminated

Advantages

• strong UV and weathering resistance
• some silicone manufacturers include ponding water in their warranties, unlike most acrylic products
• high solids content means less shrinkage between wet and dry film

Limitations

• Dirt pick-up: silicone surfaces can attract dirt, reducing reflectance over time.
• Recoating: few materials other than silicone adhere well to cured silicone, so future maintenance generally means more silicone.
• Slippery when wet, and less abrasion-resistant than polyurethanes in high-traffic areas, so walkway paths are often provided.
• Adhesion: some substrates need primers; adhesion tests on site are common.

Thickness

Like other roof coatings, silicones are specified by dry film thickness; total coating thicknesses on SPF roofs typically range from 0.5 to 1.0 mm (20-40 mils), depending on the manufacturer and warranty length.

Reflectivity

White silicone coatings are used for cool-roof restoration, and their solar reflectance and thermal emittance can be rated by the Cool Roof Rating Council. As with other light-coloured coatings, dirt and biological growth reduce reflectance over time, particularly in warm, humid climates, so periodic cleaning helps maintain performance.