Frequently Asked Questions

About the Materials

What is a white coating?
A white coating consists of a binder (usually an organic compound or silicone compound) blended with pigments and other additives to provide two main benefits: 1) protection of roof membranes, for longer roof life cycles; and 2) reflectivity of solar radiation, for lower air conditioning costs

What is an elastomer?
"Elastomer" is short for elastic polymer." An elastomer type polymer has the ability to return to its original shape after being stretched or deformed. In white coatings, the elastomer serves as the binder, i.e., the viscous, pliant material that holds pigments in suspension and makes them adhere to surfaces.
What is acrylic?

Acrylic is a generic name for all synthetic polymers derived from acrylic acid or methacrylic acid. Acrylic fibers in textiles contain at least 85% acrylonitrile. Acrylic is often used as the common name for polymethyl methacrylic (PMMA), the generic name for Plexiglas. The acrylic resins used in paints and coatings generally also contain PMMA. In acrylic paints and coatings, acrylic is a water-based plastic polymer that acts as the binder. Acrylic paints and coatings can be diluted with water, but they become water-resistant when dry.

What are the Ingredients of a white coating?
The main components of most white coatings are the binder, pigment and water. Water serves as a liquid carrier, which provides viscosity, allowing the pigment and binder to be spread on the roof as a thin coating. The majority of white coatings in use today are water-based coatings. For some white coatings, organic solvents are used as the liquid carrier. Coatings made from multiple-part resins are often blended on site and, before curing, such coatings may have sufficient viscosity to eliminate the need for a liquid carrier.

What pigments are used in white coatings?
Titanium dioxide and zinc oxide are common pigments that impart a bright white color to white coatings. Acrylic latex coatings are generally available in white and gray, with pastel and other colors also available.

What types of roofing membranes can be coated with white coatings?
White coatings can be applied to practically any roofing membrane. They are commonly applied to sprayed polyurethane roofs to provide waterproofing. They can also be applied to metal roofs, single-ply rubber roofs and modified bitumen roofs. They can even be applied to certain kinds of asphalt roofs. It is important to establish compatibility between the white coating and the underlying roof membrane.

Maintaining White Coatings

Are white coatings waterproof?
Many white coatings are waterproof but some are not. The property of permeability (perm rating) to liquid water, water vapor and other gases varies greatly, depending on the type of coating. Acrylic coatings are breathable, which means they have a high moisture-vapor transmission rate or permeability. Silicone coatings are also classified as breathable types. On the other hand, butyl rubbers, Hypalons and Neoprenes have a very low permeability, i.e., they are highly resistant to moisture transmission.

Is permeability the same as weather-ability?
No. The perm rating should not be confused with weather-ability, or resistance to weathering. A coating with low permeability still may require a protective topcoat. Likewise, a breathable acrylic latex coating may exhibit excellent resistance to weathering.

Do white coatings remain white?
Roofs that have white coatings in arid, dusty regions, or in places where farm plowing or construction exposes the earth to wind, are likely to accumulate dirt more than in areas with greenery or where occasional rainfall washes away the dirt. The frequency and intensity of precipitation and the slope of the roof also affect the cleanliness of the coatings over time. As with white paints on other surfaces, white coatings discolor and darken slightly after several years of service.

Are white coatings still effective as they age?
Two values of reflectivity are often quoted to represent the performance of new coatings and three-year-old white coatings, respectively. Generally, a small decrease in reflectivity occurs, depending on several factors. Wind-blown dirt and dust can decrease the reflectivity of white coatings, depending on the age of the coating and regional characteristics. The Sacramento Municipal Utility Division (SMUD) annually publishes data on the reflectivity of hundreds of different white coating products, which are rated for initial reflectivity and reflectivity after three years of weathering.

Does a dirty white coating still protect a roof from UV radiation?
UV radiation tends to be blocked rather than reflected by a white coating. A white coating still protects against UV radiation even when foreign particles reduce the reflectivity.

Are white coatings cleanable?
Acrylic latex white coatings tend to cure from the outside and chalk away, one thin layout after another, periodically exposing new white material to the sun's radiation. Roofs also may be periodically refreshed with a new topcoat, typically for less than the cost of the initial coating.

How often do white coatings need to be applied?
The maintenance schedule depends on the type of coating, type of roof, the purpose of the coating and regional differences. Typically, white coatings should be refreshed every three to seven years.

What surface preparation is required for a white coating?
Surfaces should be clean and dry, and they must have a positive slope to drains. Application of white coatings over dirty, wet or contaminated surfaces may produce unsatisfactory results.

What skill level is necessary for installation?
Manufacturer literature should be consulted and followed to properly prepare the surface for the coating. Professional roofing contractors should be employed for the most initial coating installations. For certain system, contractors may need to be specially trained by the manufacturer in the application of the coating. Proper application of the roof coating factors strongly in the subsequent life and performance of the coating.

What special considerations apply to acrylic latex coatings?
Since acrylic latex coatings are water soluble, they are sensitive to dew, rain and other moisture during curing. It is important that the application be done with strict adherence to the manufacturers recommendations.

How are white coatings applied?
Coatings are typically applied by spraying, rolling or brushing.