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.
Acrylic
Acrylic roof coatings are among the most durable and inexpensive elastomeric coatings in the industry. 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.
Acrylic coatings are often used to restore aged metal roofs, but they also work on a number of different roofing substrates such as 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 materials 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.
Silicone
Silicone roof coatings are the preferred choice when it comes to UV protection and resistance to ponding water. They erode much slower than other coatings without becoming brittle or hard. Modern silicone formulations have a high-solids content that typically exceeds 90 percent. This means less material is needed to achieve the required dry film thickness.
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.
Urethane (Polyurethane)
When it comes to strength, durability, and adhesion, urethane roof coatings are second to none. Compared to other coatings, they are more impact-resistant and are better suited to handle pedestrian traffic. They are also strong enough to endure the natural expansion and contraction (thermal movement) of roof structures and the negative effects of ponding water.
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.
Asphalt Emulsion
Another widely used roof restoration material is asphalt emulsion. This product consists of asphalt particles dispersed in water with clay used as a bonding element.
Generally black or brown in color, asphalt emulsion contains organic and inorganic compounds, as well as other fillers to add strength and durability.
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.
Although it can be installed as a standalone roofing material, asphalt emulsion is commonly used to provide a monolithic foundation membrane for other elastomeric roof coating systems that offer better reflectivity and UV stability.
Asphalt emulsion usually requires 3 to 4 gallons per 100 square feet depending on the substrate. Multiple passes may be required to achieve proper results.
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.
Butyl Rubber
Butyl coatings are a solvent-based polymer best known for their exceptional elongation and tensile strength. They are highly reflective, fast-drying, and great for roof maintenance and repair.
Due to their low permeability, butyl rubber coatings are most commonly used as a vapor-retardant barrier over spray polyurethane foam systems in cold storage/freezer applications.
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 disadvantage of butyl coating is its low solids content. This means it takes more liquid material to achieve a certain dry mil thickness, which makes it less cost-effective than alternative coating types.
They can also be challenging to work with and lack color stability.
