Acrylic Roof Coating

Acrylic roof coatings are water-based elastomeric coatings made from acrylic polymer emulsions with pigments, typically titanium dioxide for white products, and fillers. They dry by evaporation into a flexible film that stretches and recovers with roof movement.

Uses

• reflective cool-roof coatings over existing membranes, metal roofs and modified bitumen
• protective top coat on spray polyurethane foam roofs
• restoration of weathered single-ply and bituminous roofs, often with polyester fabric at seams and details

Acrylics are among the most widely used restoration coatings. The NYC CoolRoofs programme, for example, applied acrylic elastomeric coatings to roof membranes across New York City.

Advantages

• high initial solar reflectance in white
• easy application by spray or roller and water clean-up
• low odour and low solvent content
• relatively low cost

Limitations

• Ponding water: acrylic coatings soften and can lose adhesion under standing water, and acrylic manufacturers typically do not warrant ponding areas. Drainage must be corrected first, or a different coating used in low spots.
• Weather during application: rain, dew or freezing before the film dries can wash out or damage it, so acrylics need warm, dry conditions.
• Film build: each coat is relatively thin, so several coats are often needed to reach the specified dry film thickness.

Maintenance

Reflectance falls as dirt accumulates; cleaning and periodic recoating restore performance.

Standards and ratings

Cool-roof coatings are rated for solar reflectance and thermal emittance by the Cool Roof Rating Council, whose directory lists more than 500 coatings. ENERGY STAR criteria for low-slope roof products set minimum solar reflectance of 0.65 initially and 0.50 after weathering.