Roof Coating Type Depends on Roof Substrate

Institutional and commercial facilities for many years have used roof coatings for surfacing and restoring roofing systems. The performance of many coatings used today has improved, compared to the first coatings installed 30 years ago. This improvement is especially true when it comes to adhesion to a variety of roofing substrates, as well as long-term performance.

Specified and applied properly, coatings can extend roof life, lower cooling costs, and minimize the need for frequent repairs. These bottom-line benefits make roof coatings attractive products for managers seeking to deliver benefits to their organizations.

Coating Types

With the introduction of roof membranes such as ethylene propylene diene monomer (EPDM), polyvinyl chloride (PVC), thermal polyolefin (TPO), Hypalon, modified bitumen, and built-up roofing, manufacturers have developed a variety of roof coatings to address multiple substrates with different adhesion and weathering characteristics.

Managers can specify asphaltic and tar-based coatings for use with coal-tar-pitch built-up roof systems. Non-asphaltic coatings, including urethanes, acrylics, and polyureas, are most commonly used on single-ply systems.

Each of these coatings has different cost and performance factors. Due to variations in coating formulations, a manager should work closely with a roof consultant and the manufacturer to make sure they specify the right coating for the roof substrate and that workers perform the correct repairs before applying the coating. Manufacturer representatives and product data sheets also can assist in specifying coatings.

Roofs are expensive to maintain and even more expensive to replace. As part of an aggressive maintenance program, roof coatings applied to a roof system in relatively good condition can extend the system’s service life for many years, delaying replacement.

Coatings provide a renewable surface that protects the underlying membrane from exposure to ultraviolet (UV) light and heat, slowing the roof’s aging process. Highly reflective white coatings also significantly reduce the membrane’s temperature, which leads to improved long-term performance of the system. This lower temperature also reduces the building’s heat load, resulting in lower cooling costs for the building.

Reflective coatings can reflect 60-85 percent of solar energy. But managers should be aware that solar reflectance changes as a coating ages. A high-quality reflective coating can quickly pay for itself in energy savings. White roofs have a tendency to collect dirt, and the amount of dirt typically depends on the roof’s slope, weather conditions, rainfall, and surrounding elements.

Annual walk-overs of the roof system often reveal these conditions. Managers also can schedule crews to power-wash dirty areas regularly and apply an additional coating layer.

Many available coatings contain good waterproofing materials, but seams, fasteners, and areas around penetrations, such as vents and HVAC equipment, require special attention to prevent leaks. Some manufacturers recommend using polyester fabric with their coatings and patching mastics.

Trowel-grade mastics, along with reinforced fabric mesh, can seal seams and other potential leak areas. Self-adhesive tape systems also are available for metal and single-ply systems. These tapes are expensive but offer labor savings, making them acceptable alternatives.

Workers generally can apply coatings easily and quickly over an existing roof surface, but the hardest part of the job often is surface preparation and the repairs required before the application can take place. Again, preventive measures offer benefits: A smaller workforce can perform the repairs and apply the coating, compared to installing a new single-ply, built-up, or metal-roof assembly.

Coatings also can be effective in reducing and controlling corrosion on metal roofs. Where rust exists, crews must completely remove it and use a rust-inhibiting primer or asphalt coating to slow or stop its spread.

Finally, many coatings are environmentally responsible, and workers can apply them with little disruption to facility operations. Using coatings also can help organizations minimize construction debris that results from roof tear-off and replacement.

Before undertaking a roof-restoration project, managers need to thoroughly understand the existing roof conditions and let these conditions dictate their selection to ensure common repair problems from reoccurring. Open seams, cracks, blisters and other deficiencies require repair before the coating application can begin.

Using infrared technology can help locate wet insulation, which is important because failing to remove wet insulation can lead to advanced deterioration of the membrane and insulation and eventually damage to the deck. Once workers remove the wet insulation and install the new membrane, they can begin surface preparation and the coating application.

Proper preparation of the roof surface is essential before applying any roof coating, and the level of preparation depends on the current condition of the roof. Preparation might be as simple as sweeping, priming and repairing seams.

The surface to be coated must be clean and dry, or adhesion will not occur. If the selected roof coating does not properly adhere to the surface, the coating eventually will disbond from the surface, resulting in an unsuccessful project.

Using a primer is recommended for most surfaces and might be required by the manufacturer before applying the elastomeric coating. In multi-coat applications, workers should apply the base coat at the manufacturer’s recommended film thickness. They should apply the topcoat perpendicular to the base coat, which helps minimize irregularities caused by roller marks.

On days where humidity is low and outside air temperatures are moderate, the elastomeric coatings dry fairly rapidly. On days where precipitation is likely, workers should not install the coating, due to potential run-off.

Today’s elastomeric roof coatings are formulated for use with different types of application equipment, including high-pressure airless sprayers, rollers, and brushes. Whatever the method, workers should monitor application rates with a wet-film-thickness gauge to ensure the proper amount of coating goes on the surface.

Many manufacturers offer 5-, 10-, and even 15-year warranties on their coatings. But the existing roof substrate typically is not a coating manufacturer’s product, so it is not part of the roof warranty.

During a project’s design and construction, the coating manufacturer might require test cut samples of the membrane before selecting and applying a coating. The attachment of the existing roof system also might affect the type of warranty the manufacturer chooses to provide.

Using an elastomeric roof coating in conjunction with a professional roof-management program, managers will find they can recoat a roof numerous times before having to replace the initial roof membrane. With proper maintenance and coatings, a roof can last much longer than its design life, creating significant savings for the organization.

Roof Restoration and Coating Benefits • Lower energy cost • Increased service life • Quick and easy application • Aesthetics • Minimize business disruption • No tear-off or landfill fees • Cost-effective over second roofing layer • Restoration usually can be repeated • Less work, smaller crews, lower labor costs • Environmental friendliness • Additional warranty protection.

 Contact Gwinnett Commercial Maintenance at 770-995-0072 for more information about roof coatings and a free estimate to evaluate your commercial roof needs.