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 are seamless and when installed correctly, can solve roof leaks on almost any type of roof substrate.
There are exceptions: "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." 
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.
However, coating asphalt shingles and built-up composition roofs requires more caution.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." 
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 on the right shows "175°F" on the uncoated (black) section of the modified bitumen roof. The coated (white) section is "79°F". Field studies have shown that cool roof coatings can lower rooftop temperatures and reduce air conditioning bills.
Roof coatings are easy to install. Smaller roofs in good, serviceable condition can be a weekend DIY project. Larger roofs with leaks and ponding water issues should be restored by a qualified professional.
Tools and equipment
High Pressure Airless Spray Equipment, Pressure Washers with rotary (turbo) nozzle, roof repair equipment and basic painting tools such as brushes, rollers, putty knives. Scaffolding
- “Cool Roofs” chapter of EPA’s Reducing Urban Heat Islands: Compendium of Strategies Page 19 “4.3 Installation and Maintenance”
- "Myth busting" Maciek Rupar, Professional Roofing, Professional Roofing / National Roofing Contractors Assn, 4/2010, Page(s) 36-39