Roofing Preparation for White Roof Coatings

Function

• A white roof coating contains binders and other additives that help protect a roof's surface and reflect solar heat to keep the roof cooler. The RCMA notes that white coatings can increase your roof's ability to shed water to prevent wood rot and other moisture damage. They also can reduce your energy bills, because a cooler roof means less heat infiltrates your home. Your roof may last longer, too, because white coatings reduce stress on roofing materials associated with the expansion and contraction that results from swings in temperature.

Roofing Materials

• Find out whether a white coating will adhere to your roofing materials before you apply it. The coating usually adheres to sprayed polyurethane roofs and metal or rubber roofing materials. Directions from coating manufacturers will show the appropriate surfaces for specific products. The RCMA indicates that a white coating can sufficiently cover some asphalt shingles, but you should check with the shingle and coating manufacturers to predetermine if your shingles are compatible with a coating. Check your roof warranty to find out if applying a coating to your shingles will void the manufacturer's warranty.

Repairs and Cleaning

• Elastek is one of several brands of white roof coating, and the manufacturer notes that cracks, tears and other damage to a roof's surface need repairing before the coating is applied. However, the company warns that white coatings won't extend the life of roofs that are worn out. Elastek instructions recommend using a broom to clean the roof with trisodium phosphate before applying the coating. TSP is an all-purpose cleaner used to remove grease and dirt before painting various surfaces.

Primers

• The manufacturer of the white coating you choose may recommend applying a primer to the roof before you apply the coating. Primers usually boost the adhesion of coatings, but they also prevent coatings from soaking through a surface. In any case, SolarEstimate.org notes that white roof coatings initially reflect up to 80 percent of the sun's light, so only about 20 percent of the sun's energy gets absorbed as heat. However, a coating will degrade over time no matter how well you prepare the roof's surface before applying it. A coating’s reflectance may drop to 50 percent after several years, according to SolarEstimate.org.