Heat blisters have always been a concern when applying a dark-colored, high-build elastomeric roof coating during the hot summer months. Because elastomeric coatings dry from the top down, the excess heat causes the coating to skin over at an accelerated rate. The escaping moisture then becomes trapped and ultimately forms a blister.

In the summer of 2018, an American WeatherStar Platinum Level contractor was installing the Met-A-Gard+ system on a factory-painted metal roof in Jacksonville, Florida.

Project Details:
  • Roof Type: Standing-seam metal roof
  • Roof Size: 150,000 sq. ft.
  • Project Timeline: March-July 2018
  • Roof Surface Temperature: As high as 170°F
  • Coating Used: High-Tensile Acrylic 211 (tinted dark-brown)

With knowledge of our concern, our chemist added a proprietary component to the High-Tensile Acrylic 211 that was to be used on the project. We knew that on a project of this magnitude, there was a strong chance the job would run well into the hot summer months. There was an enormous amount of detail work and priming needed before the modified High-Tensile Acrylic 211 could be installed. Out of concern, the contractor informed the building owner of the possible delay.

Even with the additive, blisters began to form on the surface at temperatures around 130°F. After consulting with the contractor and chemist, we decided to send the contractor more of the solution to add to each drum before spraying. The increase went from 1% up to as much as 3%. While this may not sound like much, it made an incredible difference in the performance of the coating. The contractor reported that the coating did dry fairly quickly in the extreme heat, but no blistering had occurred.

Repairs were needed to fix areas of the roof affected by blistering. The first step was to cut out each blister and coat over it with Acrylic Butter-Grade 221 (white). To complete the repair, a dark brown-tinted coat of High-Tensile Acrylic 211 was then applied.  The lessons learned on this project offer best practices on how to formulate dark-tinted coatings for summer month projects.

Metal Roof