Facility Maintenance Decisions

Roof Coating Performance Depends on Application, Preparation

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:

  • Acrylic coatings are breathable, so they have a high moisture-vapor transmission rate, or permeability.
  • Silicone coatings are classified as breathable.
  • Butyl rubbers, hypalons and neoprenes have very low permeability, so they are highly resistant to moisture transmission.

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.

Coatings and Cleanliness

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).

Spotlight: Roof Coatings
Manufacturers Association (RCMA)

The Roof Coatings Manufacturers Association (RCMA) is the national trade association representing the manufacturers of cold-applied coatings and repair products for use in roofing and waterproofing, encompassing a wide variety of engineered coatings.

Founded in 1982, RCMA is dedicated to the advancement of the roof coatings industry by sharing product knowledge and technology that keep our members and their customers up to date with current trends, regulations, and building and energy codes that promote the use of roof coatings.

RCMA regularly interfaces with members of Congress, the U.S. Environmental Protection Agency, Energy Star, and building-code bodies to assist in developing credible, fact-based information and guidelines for the use of the sustainable and energy efficient products we represent.

You can contact RCMA at questions@roofcoatings.org.

Continue Reading: White Roof Coatings: Application Insights

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Roof Coating Performance Depends on Application, Preparation

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  posted on 9/30/2011   Article Use Policy

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