Roof coatings have been used to surface and restore roofing systems for decades. Many coatings used today have improved in performance compared to the first coatings applied 30 years ago. This improvement is especially true in terms of adhesion to a variety of roofing substrates, as well as long-term performance.
With the introduction of roof membranes such as EPDM, PVC, TPO, Hypalon, modified bitumen, and built-up roofing, manufacturers have developed a variety of roof coatings to address multiple substrates that have different adhesion and weathering characteristics.
Managers can specify asphaltic coatings for use on asphalt and coal-tar-pitch, built-up roofing systems. Non-asphaltic coatings such as urethanes, acrylics, and polyureas, are most commonly applied to single-ply roof systems.
Each coating has different cost and performance factors. Due to variations in coating formulations, managers should work closely with a roof consultant and the manufacturer to ensure that they specify the most appropriate coating for the roof substrate, and that technicians perform repairs correctly before the coating application.
Roofs are expensive to maintain, but they are even more expensive to replace. With an aggressive maintenance program, technicians will be able to apply a coating to a surface that is in relatively good condition as a way to extend the roof’s service life for many years and put off expensive roof replacement.
A coating provides a renewable surface that protects the underlying membrane from exposure to heat and ultraviolet (UV) light, slowing the roof’s aging process.
Highly reflective white and light-colored coatings can reduce the temperature of the roofing membrane significantly, which leads to improved long-term roof performance. This lower temperature also reduces the heat load in the building, resulting in lower cooling costs. Reflective coatings can reflect 60-85 percent of solar energy, and a quality reflective coating can pay for itself in energy savings.
Trowel-grade mastics, along with reinforced fabric mesh, help to seal seams and other potential areas of leaks. Self-adhesive tape systems for metal and single-ply roof systems can be expensive, but their potential labor savings making them acceptable alternatives.
Coatings also can be an excellent way to reduce and control corrosion. A rust-inhibiting primer or asphalt coating might slow or stop the spread of rust. Many coating manufacturers also offer coatings in a variety of colors, allowing managers to selected a coating that blends in with other building components.
Roof coatings typically are environmentally friendly, and they can be applied with little disruption of facility operations. Also, managers can use a smaller workforce to perform repairs and apply the coating, compared to the crew needed to install a new roof.
Coatings can be applied relatively quickly and easily over an existing roof surface, but surface preparation and repairs required before an application takes place can be the hardest — and most important — component of the project.
The surface to be coated must be clean and dry, or adhesion will not take place. If the selected roof coating does not properly adhere to the surface, the coating eventually will disbond.
The level of preparation will depend on the current surface of the roof. Preparation might be as simple as sweeping, priming, and seam repairs.
Before performing any roof restoration project, it is essential to thoroughly understand existing conditions and use those conditions to dictate the recommendations as a way to avoid the common problems from reoccurring. Open seams, cracks, blisters, and other deficiencies require repair before any coating application.
It is vital to perform an infrared survey to identify wet insulation. Failure to remove wet insulation could lead to advanced deterioration of the membrane and insulation, and eventually it could damage the deck. Once wet insulation is removed and a new membrane installed, surface preparation and coating can begin.
Annual walking inspections of the roof system can help detect problem areas. Many coatings are excellent waterproofing materials, but seams, fasteners and areas around penetrations — including those for vents and HVAC equipment — require special attention. Some coating manufacturers recommend using polyester fabric and patching mastics with their products.
White and light-colored roof surfaces tend to collect dirt, a situation that typically depends on roof slope, weather, rainfall, and surrounding elements. Also, a solar reflectance will change as the coating ages. A manager might elect to have workers pressure-wash dirty areas occasionally and apply additional layers of coating.
Most surfaces will benefit from using a primer, and manufacturers might require it before applying an elastomeric coating.
Technicians must apply the base coat at the manufacturer’s recommended film thickness. It often is pigmented differently than the primer or top coat to assist in complete coverage, and it is applied perpendicular to the base coat to helps minimize irregularities caused by roller marks.
If the humidity is low and outside air temperatures are moderate, elastomeric coatings dry fairly rapidly. But managers should keep foot traffic off the roof for several days. If precipitation is likely, managers should not apply the coating because of potential run-off.
Today, elastomeric roof coatings are formulated to work with different types of application equipment, including high-pressure airless spray equipment, rollers, and brushes. In any case, to ensure the proper quantity of coating is applied, technicians should monitor application rates using a wet-film thickness gauge.
Many coating manufacturers offer five-, ten-, and fifteen-year warranties on their products. But existing roof substrates typically are not the coating manufacturer’s product and, therefore, are excluded from the warranty.
During the design and construction of a project and before coating application, the coating manufacturer might require test-cut membrane samples. The attachment method of the existing roof system also might affect the type of warranty the manufacturer is willing to provide.
Using an elastomeric roof coating with a professional roof management program, managers will be able to recoat the roof many times before replacement of the initial roof membrane is needed. With proper maintenance and coating application, a roof can last significantly longer than its design life.
Jeffrey J. Opel is a senior project manager with StructureTec Corp. — www.structuretec.com — and specializes in major capital roof-replacement projects.