Coating applicators typically use airless sprayers, rollers or brushes. Due to the variety of coating types, climactic conditions and surfaces to be coated, it is important to consult the manufacturer for proper application rates and related recommendations.
Many, but not all, white coatings are waterproof. A coating's permeability — its perm rating — to liquid water, water vapor, and gases varies greatly, depending on the coating type:
Specifiers should not confuse a coating's perm rating with its weather resistance. A coating with low permeability still might require a protective topcoat to ensure satisfactory resistance to weather.
Roofs covered by white coatings and located in arid and dusty regions, or in places where farm plowing or construction exposes the earth to wind, are likely to accumulate dirt more quickly than roofs in areas with greenery or where occasional rainfall washes away dirt.
The frequency and intensity of precipitation, along with the slope of the roof, also affect the cleanliness of coatings over time. As with other white surfaces, white coatings can discolor and darken slightly after several years of service.
Generally, a small decrease in reflectivity occurs over time, depending on several factors. Wind-blown dirt and dust can decrease the reflectivity of white coatings, depending on the coating's age and regional climate characteristics.
A white coating tends to block, rather than reflect, UV radiation. A white coating still protects against UV radiation, even when foreign particles reduce its reflectivity.
To maintain coatings' reflectivity, managers might periodically schedule a new topcoat to refresh the surface. This typically costs less than the initial coating.
A coating's maintenance schedule depends on its type, as well as the type of roof, the purpose of the coating, and regional climate differences. Typically, workers should refresh white coatings every three to seven years to receive their maximum benefits.
These recommendations are not intended to revoke or change the requirements or specifications of individual roofing material manufacturers or local, state and federal building officials that have jurisdiction. Managers should direct questions about a coating's requirements or specifications to the product's manufacturer.
Information for this article is adapted from a technical note written by the Roof Coatings Manufacturers Association (RCMA).
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