Elastomeric roof coatings have been around for a long time. That being said, many facility owners and managers are still relatively unaware of the numerous advantages they provide. Before we get into the strengths and weaknesses of the various types of coating chemistries available in the industry, let’s get an idea of the many benefits a coating system provides, in general.
Roof replacement can be quite expensive. Depending on the type of roof you have, a full replacement can cost anywhere from $5 to $15 per sq. ft. Roof restoration, on the other hand, provides all the benefits of a new roof but for a fraction of the cost.
Because roof coatings are applied directly over existing surfaces, they require far less labor and material than traditional roof tear-offs and replacements. As a result, you can expect to pay 50-70% less by installing a roof coating system on your building.
Perhaps the best-known quality of an elastomeric coating system is its ability to extend roof life. The average commercial roof only lasts about 20 years, but the addition of a coating system can prolong a roof’s serviceable life by up to 10, 15, or even 20 years. Elastomeric coatings provide aged roof membranes with a protective, waterproof barrier that stops leaks and improves performance. If properly installed and maintained, a coating system has the potential to be recoated numerous times. It also can significantly reduce the need for constant maintenance and repair.
Coating your roof is a great way to improve the energy efficiency of your building. Unlike conventional dark-colored roofing materials, white roof coatings can reflect 80-90% of the sun’s harsh UV rays and diminish the flow of heat to your building. This reduces the workloads of HVAC systems during warm summer months and cuts interior cooling costs by up to 20% on average.
Additionally, the superior reflective and emissive qualities of a coating system can significantly cool roof surface temperatures and provide a more comfortable work environment for building occupants. Unconditioned spaces can experience a reduction in ambient temperatures, as well.
In recent years, the demand for more sustainable roofing solutions has grown considerably due to more stringent environmental regulations and building codes as well as increased concern for the environment. Commercial roof tear-offs contribute millions of tons of waste to landfills each year. In contrast, there is no tear-off required prior to the application of a commercial roof coating system, allowing you to reuse existing roofing materials with minimal impact on the environment. As mentioned above, the prospect of recoating also contributes to increased sustainability.
In addition to improved sustainability efforts, many of today’s elastomeric coatings are developed with little to no VOCs (volatile organic compounds), making them much safer for the environment. This also means buildings with a roof restoration system could qualify for the US Green Building Council’s LEED program.
Choosing the best coating for a particular roofing environment depends on a variety of factors such as roof type, age, weather conditions, environmental concerns, aesthetics, etc. Below, we take an in-depth look at some of the key strengths and weaknesses of today’s most common types of coating.
Traditionally used to restore metal roof surfaces, acrylic coatings have since evolved to work on a number of different roofing substrates including modified bitumen, single-ply, built-up roofs, and spray polyurethane foam. Acrylics are easy to work with and come in a variety of different standard, premium, and custom colors. These coatings can be spray or roll-applied at a rate of .75 to 1.5 gallons per 100 square feet, depending on the substrate.
Acrylics do not stand up well to ponding water and are only recommended for roofs with positive drainage. Cold temperature applications can also be a problem. Because acrylic is a water-based substance, temperatures at or below 50°F can negatively affect adhesion to the roof substrate and impede cure time.
Asphalt emulsion is inexpensive and easy to work with. It is typically used to level “alligatoring” and other irregularities that commonly occur on modified bitumen and built-up roof surfaces.
Asphalt emulsions are a water-based product, which makes them susceptible to freezing temperatures. They can also be very difficult to work with during cold weather conditions.
While it can be installed as a stand-alone roofing material, an asphalt emulsion is most commonly used to provide a monolithic foundation membrane for other elastomeric roof coating products that have better reflectivity and UV stability. They generally require 3 to 4 gallons per 100 square feet depending on the substrate. Multiple passes may be required to achieve proper results.
A butyl coating system is suitable for a variety of commercial roof surfaces including metal, modified bitumen, single-ply, built-up roofs, and spray polyurethane foam. They are typically white, gray, or tan in color and can be sprayed or roll-applied at a rate of about 2 gallons per 100 square feet.
The primary disadvantages of butyl coatings are their low solids content and their lack of color stability. They require more material to achieve the desired dry film thickness, making them less cost-effective than other elastomeric coatings. They can also be challenging to spray and difficult on application equipment.
Silicone coatings are created by adding solvents and a catalyst to a silicone base. Available in white, gray, or tan, silicone can be installed on a variety of roof types including metal, modified bitumen, single-ply, EPDM, built-up roofs, and spray polyurethane foam. Depending on the substrate, most silicone roofing systems require multiple coats at 1.5 gallons per 100 square feet.
Silicones attract dirt rather easily. This means the system will gradually lose reflectivity over time if not cleaned periodically. They are also extremely slippery when moisture is present. Resistance to tearing is another inherent weakness. If pedestrian traffic is expected on the roof, we highly recommend incorporating roofing granules into the system.
There are two main types of urethane coatings: aliphatic and aromatic. Aliphatics are generally used as top coat, as they are more UV stable, resistant to dirt pick-up, and have superior color retention. Aromatics are less expensive but not quite as UV stable. They are primarily used as a foundation coating in most roof restoration systems. Both types can be spray or roll-applied, with most system specifications requiring multiple coats at a rate of 1.5 gallons per 100 square feet.
Being a xylene-based material, urethane coatings can be challenging to spray, harsh on installation equipment, and highly odorous. It’s also worth mentioning that urethanes are a moisture-cure coating, meaning they are constantly curing—even in the pail.