Which Roof Coatings Work Best?
With so many different types of roof coatings available in today’s market, how do you determine which one is the best solution? To be honest, there is no clear-cut answer to that question. There are a number of factors that go into determining which roof coating is the best solution such as roof type and age, weather conditions, environmental concerns, aesthetic standards, etc.
Below, we examine some benefits and limitations of today’s most common types of roof coatings. To learn more about the growth of the roof coatings market in the United States, click here.
Acrylic Roof Coatings
Often referred to as the “original” elastomeric coating, acrylic roof coatings are among the most durable and inexpensive types of roof coatings available in today’s market. Comprised of high solids emulsion polymers and potent biocides, these highly-reflective coatings are ideally suited for extreme UV climates and provide superior resistance to mildew and dirt accumulation.
Traditionally used to restore metal roof surfaces, acrylic roof coatings have since evolved to work on a number of different substrates such as modified bitumen, single-ply, smooth BUR, and spray polyurethane foam (SPF). Acrylics are easy to work with and come in a variety of different standard and custom colors. These coatings can be sprayed or roll-applied—typically at a rate of .75 to 1.5 gallons per 100 square feet, depending on the substrate.
Acrylic roof coatings do not stand up well to ponding water and are only recommended for roofs with positive drainage. By better understanding the negatives of acrylic roof coatings, our contractors can improve overall system performance, increase longevity, and avoid any potential problems. Cold temperatures can also be a problem during application. Because acrylics are a water-based product, temperatures at or below 50°F can negatively affect adhesion to the roof substrate and severely impede cure time.
Another widely popular roof coating is asphalt emulsion. This coating consists of asphalt particles dispersed in water with clay used as a bonding element. Generally black or brown in color, these coatings contain organic and inorganic compounds, and other fillers to add strength and durability.
Asphalt emulsions are inexpensive and easy to apply. This coating is typically used to level “alligatoring” and other irregularities found on modified bitumen and built-up roof surfaces. While it can be installed as a stand-alone repair product, it is most commonly used to provide a monolithic foundation for coatings with better reflectivity and UV stability. This coating requires 3 to 4 gallons per 100 square feet depending on the substrate, however, multiple passes may be necessary to achieve proper results.
Asphalt emulsions are a water-based product. This makes them susceptible to freezing temperatures and can be very difficult to work with in cold weather conditions.
Butyl Roof Coatings
Butyl roof coatings are best known for their extremely high elongation and tensile strength. This solvent-based polymer is highly-reflective, fast-drying, and works great for repairs. Due to their low permeability, these coatings are most commonly used as a vapor-retardant barrier over spray polyurethane foam systems in cold storage/freezer applications.
Butyl roof coatings are suitable for a number of commercial and industrial roof surfaces including metal, modified bitumen, single-ply, smooth BUR, and spray polyurethane foam (SPF). These coatings 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 drawback of butyl roof coatings are their low-solids content. This means they require more material to achieve the desired dry film thickness, making it less cost-effective than other types of roof coatings on the market. It can also be challenging to spray and harsh on installation equipment.
Silicone Roof Coatings
Silicone roof coatings are among the most popular in the industry—and for a number of reasons. They are the best choice when it comes to UV stability and resistance to ponding water, and they erode much slower than other coatings without becoming brittle or hard. In some applications, the use of silicone can eliminate the need for a primer. Modern silicone formulations have a high-solids content that typically exceeds 95 percent. This means less material is needed to achieve the required dry film thickness.
Silicone roof coatings are created by adding solvents and a catalyst to a silicone base. Available in white, gray, or tan, silicone roof coatings can be installed on a variety of different roof types including metal, modified bitumen, single-ply, smooth BUR, and spray polyurethane foam (SPF). Most silicone systems require multiple coats at 1.5 gallons per 100 square feet depending on the substrate.
Silicone roof coatings attract dirt very easily. Therefore, the system will lose reflectivity over time if not cleaned regularly. Silicone coatings also get very slippery when wet. If pedestrian traffic is expected on the roof, we highly recommend incorporating roofing granules into the system. Resistance to tearing is another inherent weakness of silicone coatings.
Click here to learn about the best practices of working with silicone roof coatings.
Urethane Roof Coatings
When it comes to strength and durability, urethane roof coatings are second to none. Urethane coatings are more impact-resistant and handle traffic better than any other type of roof coating. They are fast-drying, UV resistant, and have excellent adhesive and cohesive strength. These highly-flexible coatings can withstand the normal expansion and contraction (thermal cycling) that occurs on commercial and industrial roof structures.
There are two main types of urethane roof coatings: aliphatic and aromatic. Aliphatic urethanes—which are generally used as top coat—are more UV stable, resistant to dirt pick-up, and have better color retention. Aromatic urethanes are less expensive and not quite as UV stable. Therefore, it is primarily used as a foundation coating in some roof restoration systems. Both types can be sprayed or roll-applied, with most systems specifications requiring multiple coats at a rate of 1.5 gallons per 100 square feet.
Xylene-based urethane roof coatings can be challenging to spray, harsh on installation equipment, and produce strong odors. It’s also worth mentioning that urethanes are a moisture-cured coating. This means the product is always curing—even in the pail.