Roof coatings: for better or worse

With all the hype from the U.S. Department of Energy, Environmental Protection Agency, California Energy Commission and others about energy-efficient roof systems, have come a wide variety of generally acrylic-based white roof coatings out of every corner of the roofing industry and most corners of the coating and paint industries. Comparative testing indicates not all roof coatings are equal—some perform much more admirably than others. Preparing surfaces to which coatings are to be applied remains the most important step in the coating process to ensure relatively long service life. Carefully evaluating surfaces over which roof coatings are to be applied runs a close second.

Performance

Roof coatings are much like paint—the more polymer "solids" per gallon, the longer the coating's potential life. The more aluminum "metal" (not paste) in asphalt-based aluminum roof coatings, the better the potential long-term performance. Likewise, the more acrylic polymer in a water-based roof coating, the better the potential long-term performance. But the "best" roof coatings available will not live up to expectations if surfaces to which they are applied have not been evaluated for adhesion and surface preparation does not provide a suitable base for the coating. Solvent-based coatings are a little more forgiving of improperly prepared roof surfaces than are water-based coatings simply because the solvents provide a modicum of "self-priming" properties. Simply adding a "catalyst" (in two-component coatings) to the coating does not necessarily ensure better adhesion or weathering performance.

The primary qualities necessary for an acceptable roof coating are:

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