Q&A - What is the recommended temperature range for primer application?

A homeowner wanted to know the recommended temperature range for applying primer to their roof, as well as advice on sun exposure and top coats.

Gregg, a homeowner preparing to repaint their roof, wanted to know the recommended temperature range for primer application. They asked: 

I am using HP-Primer. In what temperature range can it be used? How long can it be exposed to the sun prior to top coat application? What top coat do you recommend?

Roofing expert John Kenney of Cotney Consulting Group had this to say in response:

Each manufacturer may be slightly different, so you should follow their installation recommendations. I am going to provide you with a generic answer as a guideline.

1 - Recommended temperature range for application

HP Primer should be applied when ambient and surface temperatures are 50°F (10°C) and rising. This ensures optimal adhesion and curing conditions. Avoid application during high humidity or when rain is expected within 24 hours.

2 - Maximum sun exposure before topcoat application

After applying, the primer develops a skin in approximately 30 minutes and achieves full cure in three to four hours under ideal conditions. It's recommended that the topcoat be applied within 24 hours of primer application to ensure optimal adhesion. Delays beyond this period may necessitate re-priming the surface.

3 - Topcoat selection and application guidelines

The appropriate topcoat will be selected based on the type and condition of the roof surface, including metal, TPO, EPDM, SBS-modified bitumen or other approved substrates. Each surface requires a compatible coating system to ensure optimal adhesion, durability and weather resistance. Once the surface is properly prepared and primed, the topcoat should be applied in two uniform coats using a roller, brush or airless sprayer. Coverage rates typically range from 1 to 1.5 gallons per 100 square feet per coat, depending on the specified product and desired dry film thickness. The second coat should be applied perpendicular to the first after fully dries the initial layer. Total system thickness and cure time will vary by product, temperature and environmental conditions. Always follow the manufacturer's product data sheets for surface-specific recommendations and application procedures.

Continue the conversation in our Forum!