How long should my roof coating last?

This is a question every facility manager or building owner needs answered during the process of evaluating any coating is right for his/her building.

There are a variety of types of coatings, usually differentiated by their chemistries. These include water borne acrylics, silicones (including the high solids version), polyurethanes, and thermoplastic butyls to name the most popular.

For all sloped metal roofs, where no ponding water may be present, acrylic coatings have been used successfully for decades. For low slope, single ply membrane or asphalt based systems where ponding water conditions may be present; the non-water based chemistries perform best.

The actual service life of the coating will be directly to application rates and resulting dry film thickness (DFT), measured in mils (1 mil = .001 inch). Logically, the thicker the coating, the longer the service life will be. Industry standard DFT has been at least 20 mils. As a reference, most credit cards are 30 mils thick.

A 10-year coating warranty, typically giving owner assurances against leaks, has been an industry standard for the past 30 years. In recent years, as the market for roof coatings has grown, and competitive forces have also further developed as players sought greater market share. One of the resulting effects is extended warranties being offered; 15, 20, 30 and even a 50 year warranty have been seen marketed.

The important approach for any owner is to understand that any warranty should be a function of proven product performance, not just s leading sales tool. Most coatings at 20 mils have proven to be effective for 10 years.