A roof coating is a monolithic, fully adhered, fluid applied roofing membrane. It has elastic properties that allows it to stretch and return to their original shape without damage.
Typical roof coating dry film thickness vary from paint film thickness (plus or minus 3 dry mils) to more than 40 dry mils. This means a roof coating actually becomes the top layer of a composite roof membrane and underlying system. As such, the roof coating is the topmost layer of protection for the membrane, receiving the impact of sunlight (both infrared and ultraviolet (UV), rain, hail and physical damage.
Roof Coatings should not be confused with deck coatings. Deck coatings are traffic bearing - designed for waterproofing areas where pedestrian (and in some cases vehicular) traffic is expected. Roof coatings will only waterproof the substrates but will not withstand any kind of on going use by people or vehicles (such as walkways, patios, sundecks, restaurants, etc.).
Roof coatings are seamless and when installed correctly, can solve roof leaks on almost any type of roofing material. Professionals do not recommend using cool coatings over existing shingles. This technique can cause moisture problems and water damage because the coating can inhibit normal shingle drying after rain or dew accumulation, allowing water to condense and collect under the shingles.
The National Roofing Contractors Association’s (NRCA) director of technical services has stated, "The roofing industry is aware of a number of issues that could have negative consequences for field application of coatings over asphalt shingle roof systems. Anyone considering this type of application should be aware of the concerns so they can weigh them against the benefits claimed in coating product promotional materials."
Field-applied reflective roof coatings can extend the useful life of nearly every roof substrate keeping a roof surface cool and providing a level of protection from the sun and weather.
Roof coatings can add 25 years to the service life of a roof and reduce the amount of discarded roofing materials that end up in landfills. The infrared image below shows 175 °F (79 °C) on the uncoated (black) section of the modified bitumen roof. The coated (white) section is 79 °F (26 °C). Field studies have shown that cool roof coatings can lower rooftop temperatures and reduce air conditioning bills.