Primer Temp Range

Gregg is asking the following: I am using HP-Primer. What's the temp range for the primer? How long can it be exposed to the sun prior to a top coat. What top coat do you recommend.

Below is what our roofing expert John Kenney of Cotney Consulting Group had to say in response to your question:

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 3–4 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.

Below is what our roofing expert Henry Staggs from The Arizona Roofer had to say about your question:

HP-Primer - Temperature Use Range

• Application Temperature: Typically 40°F to 120°F(4°C to 49°C).
• Surface must be dryand free from dew or frost.
• Avoid applying in freezing temperatures or when rain is imminent.

Exposure Time Before Topcoat

• Maximum exposure time: Generally 7 to 14 days, depending on brand and environmental conditions.
• After that window, you may need to re-primethe surface.
• If exposed too long, dirt, UV, and oxidation can affect adhesion.

✔️ Pro Tip: Always apply the topcoat as soon as the primer has flashed off and is ready, usually within 2 to 6 hours, but this depends on ambient temperature and humidity. Check the technical data sheet (TDS) for your specific HP-Primer brand.

Recommended Topcoats
This depends on what system you're working with. Here are some trusted options:

1. 
   For Polyurethane Foam or General Roof Restoration

• Acrylic Topcoat: Like Metacrylics, GAF TopCoat, AcryShield, or Tropical 924
• Ideal for reflective, water-based systems
• Requires re-application in about 10 years
• Silicone Topcoat: Like GE Enduris, GacoSil, or Astec Re-Ply Silicone

• Best for ponding waterareas
• Long-lasting and more UV stable
• More expensive, but excellent adhesion to HP-Primed surfaces

Recommendation:

• For Arizona and flat roof systems, siliconeis often the better choice due to its UV resistance and durability under ponding water.