Thursday, June 21, 2012

Explaining the three types of roof coatings

There are three general categories of roof coatings including traditional, reflective and maintenance.

Traditional roof coatings have been used for decades and are designed to be compatible chemically with the existing roof system. By protecting it from direct exposure to UV light, water and other weather elements, traditional coatings extend the servicable life of the existing roof.

Reflective roof coatings also protect the roof from exposure to sunlight and weathering, but with the added benefit of reflecting infrared heat. Even small reductions in roof surface temperature significantly extends the life of the existing roof, especially for well-insulated roof systems which get hotter because heat is retained on the roof surface.

Reflective coatings come in water-based white acrylic roof coatings and reflective aluminum asphalt. Acrylic roof coatings reduce infrared heat absorption in the roof membrane, helping to reduce the internal temperature of uninsulated buildings. This saves on cooling costs.

Water-based white acrylics must be selected carefully. For example, to use a white coating on an asphalt roof, you must specify a coating formulated specifically for asphalt. More so than other coatings, water-based white acrylics are not intended for use in standing water. If a roof has a tendency to pond, the roofing contractor should first fill the depressions where ponded water accumulates before applying an acrylic coating. Their application also is limited to emulsion surfaces, and they should not be applied at temperatures below 45 degrees. For a gravel roof, the recommendations of the manufacturer should be followed. Finally, the curing time should not be underestimated: Water-based coatings can require from six to 48 hours of cure time before the roof can be exposed to rain or cold temperatures. It is crucial that the instructions on the label are followed.

Reflective aluminum-asphalt coatings use aluminum flakes in an asphalt matrix. Although they do retain a bit more infrared heat than white coatings, they can be applied on a variety of substrates including metal, single-ply and built-up roofs. Either type of coating can be used on unpainted metal roofs, but only the aluminum-asphalt roof coatings will allow the roof to retain its metallic appearance.

Maintenance membranes use a combination of coating material and reinforcing fabric. The membranes are used either as a short-term effort to stabilize a roof that might be compromised and eventually will need to be replaced, or as a longer-term solution that can extend the life of the roof five to 15 years. But simply applying coatings is not the same as applying a complete maintenance system.


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