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In Conjunction with the Roof Coatings Manufacturers Association:
Conditions on the roof of a building can be severe. During summer months, temperatures can reach 170 degrees on a low-slope black asphalt roof, and they can drop to -20 degrees during the winter in some northern regions. Harsh conditions like this quickly break down many roof materials.
This is one reason that relatively inexpensive and replaceable roofs are so common. Some people maintain that all black or dark-colored surfaces, such as asphalt pavements and exposed black roofing materials, are contributors to a heat-island effect, by which much of the heat generated by absorbing the sun’s ultraviolet (UV) radiation transfers to the building interior.
In cooler climates, this problem can be minor. But in areas with warmer temperatures, this problem increases the demand for power, as the air-conditioning systems labor to maintain a comfortable working climate. Maintenance managers have a variety of roof coatings options to choose from in an effort to prolong a roof's performance life, minimize the effect of UV light on roofs and interior operations, and help managers control energy costs.
The Protective Layer
UV radiation and visible light from the sun repeatedly impinge upon the outermost surface layers of roofing systems, accelerating oxidation and chemically degrading the system and causing it to become brittle. As if these challenges weren't enough, rain, snow, sleet and hail further compound roof destruction through erosion, expansion and contraction forces, and mechanical impact.
Applying a roof coating on top of a conventional roofing system can act as a shield against these forces of nature. This protective coating can increase a roof's expected life cycle and improve a building’s energy efficiency. It can help roofs resist baking by the sun’s radiation, as well as chemical attack, and it can prevent the formation of small cracks that otherwise collect dirt and chemicals and grow into larger cracks.
The optical properties of protective coatings determine how well a roof reflects sunlight. Reflecting sunlight has an immediate effect; namely, lowering roof temperatures. And since chemical reactions often increase exponentially with temperature, a roof with a good reflective coating will not deteriorate as quickly as one with no coating and, hence, is exposed to higher daily temperatures.
The underlying roof might provide excellent moisture resistance in the event of rain, but a coating often is essential to protect this waterproofing agent against other forms of erosion and degradation.
Manufacturers of roof coatings offer a variety of solutions to these challenges in the form of water-based, solvent-based or hybrid roof-restoration systems. These lower-cost, high-quality maintenance systems provide maintenance and engineering managers with solutions to their needs while avoiding or delaying the higher cost of roof replacement.
Roof-restoration systems minimize disruption to businesses and offer environmentally friendly solutions that are safe and can be cold-applied. They also might provide a higher rate of return on investment via energy savings through the use of reflective coatings. High-reflectance coatings can reduce thermal shock, membrane fatigue and heating or cooling loads, which alone can lower building energy costs, especially when combined with other energy-saving measures.
Many systems have polyester-reinforced or other reinforcement scrims and can be spray-applied with odorless asphalt emulsions. In cooler weather, low-VOC solvent-based cutbacks also can be spray-applied with the use of a mechanical warmer, which allows for a longer roofing season. Roof restorations systems can be adapted to most slopes.
Among the main advantages of roof-restoration systems are the speed of application, smaller crew sizes resulting in substantial labor savings, exceptional durability when using highly permeable coatings, and the added dimensions of waterproofing and UV protection.
Another interesting aspect is the relative safety for workers of cold-applied systems. Avoiding the use of hot asphalt or torches - as well as the ability to pump emulsions or solvent-based coatings to roofs from the ground - increases the speed of application and minimizes the need for installation equipment on the roof. All of these positives lead to increased worker safety and satisfaction.
It is virtually impossible to simply look into two pails of roof coating and predict whether one product is going to perform better than another does. For this reason, specific guidelines have been established for testing and approval of liquid-applied acrylic roof coatings that provide a yardstick that can measure all products. Products that meet specific standards display that information on the label. Managers should look for such markings when evaluating a product to meet a specific need. Some markings indicate whether a coating meets specific standards or has the approval of certifying testing organizations.
Among the important standards is American Society for Testing and Materials (ASTM) D 6083. That standard measures the coating tested against specific physical performance and physical characteristics for viscosity, elongation, tensile strength, accelerated weathering after exposure to 1,000 hours of testing, permeance, water swelling, adhesion, tear strength, and low-temperature flexibility. If met, this comprehensive set of standards should lead managers to an excellent product.
Creating a waterproof barrier to atmospheric elements is the primary objective of any roof system. A high-quality roof coating will assist in this process by providing resistance to UV radiation and the effects of heavy or light rainfalls and standing and melting snow on roofs.
The ability of these coatings to stand up to the elements depends largely on the application of the properly balanced ratio of acrylic solids to fillers in the coating, the thickness at time of application, and, of course, proper roof preparation and workmanship.
Workmanship is a key variable that has a significant effect on the success of the roof-coating project. If technicians do not reinforce pipes, soffits, drains and other roof details with fabric or high-strength mastic-grade material before the final application of a coating, the risk of failure at these detail areas increases.
Also, if the condition of the existing roof is such that its structural integrity is compromised or that patching and re-coating no longer will abate the problem, applying an acrylic roof coating most likely will not solve the problem. In that event, roof replacement might be necessary.
The benefits of using of acrylic roof coatings produces cost savings for roof maintenance and energy expenditures and results in significant environmental benefits.
White Coatings: Clearing up Questions
Liquid-applied white roof coatings reflect the sun's ultraviolet radiation from a roof's surface to varying degrees. Some products are more effective than others, some hold up better over time, and some have modern technology additives that might give a product enhanced performance. Here are answers to some frequently asked questions.
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: protection of roof membranes for longer roof life cycles; and reflectivity of solar radiation, for lower air conditioning costs.
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.
On what types of membranes can white coatings be used?
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.
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. Just because a coating has a higher perm rating does not mean that it will not protect the underlying roof surface, and in some cases such as a foam roof it is desirable to have a coating with a higher perm rating.
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. Both Energy Star and the CRRC publish reflectivity numbers that the consumer can use to make an educated decision on the products to use.
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 layer after another, periodically exposing new white material to the sun's radiation. Roofs also may be periodically refreshed, by washing or applying 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.
— Roof Coatings Manufacturers Association
Spotlight: White Coatings Council
The RCMA White Coatings Council services the producers and suppliers of acrylic or elastomeric (non-bituminous) coatings. The council has implemented an industry promotional program and is actively planning programs to respond to targeted governmental and regulatory issues, technical matters and activities, and membership services and programs.
For more information, call RCMA at (202) 207-0919 or visit roofcoatings.org
The Roof Coatings Manufacturers Association provided information for this article.