September 2009 Volume 1 Number 9
Highly reflective white top coats have become more common during the past several years as a means to reduce peak roof surface temperatures. This minimizes peak electrical demand for air conditioning in many buildings and provides ultimate reduction in temperature swings, which can stress and fatigue roof systems.
A majority of these white coatings are water-borne acrylic coatings. Most white acrylic coatings intended for use on asphalt roof systems can be applied directly to mineral cap sheets after appropriate surface cleaning and preparation. Smooth asphalt surfaces normally require a specified primer or base coat designed specifically to stop asphalt from bleeding into the top coat.
Steel, aluminum and galvanized metal roof systems are good candidates for coatings. Aluminum, acrylic, urethane and polyurea are all suitable coating for metal roofs.
Urethane coatings and more recently, polyurea coatings, are two component coatings that are well suited most all roofs. They provide good elongation and high tensile strength – about 1500 pounds per square inch (psi) compared with 200 – 400 psi for other coatings. They also provide a harder surface than other types of coatings.
The urethanes and polyureas also add protection from ponded water areas, as opposed to the other coating systems. Urethanes have been used extensively for pond and fountain liners.
There is no doubt that coatings prolong roof systems’ life cycles. It may be possible to extend certain roof systems’ life cycle indefinitely by protecting substrates that age slowly and have long lives without the benefit of protective and reflective coatings.
The key factor is keeping the system maintained and dry. A good start is a bi-annual inspection and maintenance program.
Have a question? Call us, we’ll be glad to discuss coatings or any other roofing and sheet metal needs you may have.
Don’t forget our dedicated Service Department and crews. Leak response when you need it!
Last month we discussed the basics about roof coatings. One important area is to establish the coating’s intended use. After you establish the function you want the coating to perform, you must consider the type of roof system being coated and the details on that particular roof. The following provides some insight regarding coating requirements for specific roof systems.
The workhorse of the industry is the built-up roof (BUR) system. Coatings most commonly used on BUR systems include solvent and water-borne asphalt coatings; solvent and water-borne aluminized asphalt coatings; and water-borne white elastomeric coatings (usually acrylic).
BUR systems can have several surface finishes. They can have bare or glaze coated top sheets; be flood coated with mopped asphalt; have a mineral (granulated) cap sheet as a top layer; or have a finish layer of gravel embedded in hot asphalt.
A mineral cap sheet generally is the easiest surface to coat because its small texture allows most coatings to achieve a strong mechanical grip. Smooth BUR systems are readily coated with solvent-borne asphalt coatings. They require careful preparation and base coats to accept water-borne coatings. Gravel covered roofs generally are impractical to coat without removing the gravel.
Asphalt coatings, long recognized as effective for prolonging life cycles and restoring aging BUR systems, are applied after a BUR system’s initial installation and at regular intervals during the BUR system’s life cycle as part of a regular maintenance program.
Aluminum pigments can be used to formulate solvent and water-borne asphalt coatings to protect against ultraviolet (UV) radiation and provide significant reflectivity. These coatings have small flakes of aluminum pigment dispersed in them. They typically have solar reflectance of 0.40 & 0.50, though some premium formulations have shown reflectivity in excess of 70%
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