Building owners and facility managers should be aware that there have been significant changes in the uses of roof coatings on commercial roof applications over the years. These changes in the material formulations and uses of roof coatings, which began in the mid-1990s and continue today, can be linked to environmental concerns and technical advances.
The Energy Star Program, developed in the mid-1990s, required all low-slope roof systems to have a reflectivity rate of .65 to .70 after three years of application. The only way for most membranes to achieve this rating was with the application of a top coating. Coating colors were primarily white or tan, as studies had indicated that lighter colors provided better reflectivity than darker colors. The coatings were applied at a minimal rate to provide a film surface to act as a barrier against the sun’s ultraviolet rays.
Recent advances in coating material technology have increased the uses for roof coatings in the commercial market, and coatings are no longer solely viewed as reflective surfacing. Today, coatings are manufactured as monolithic, fully adhered, elastomeric materials. Coatings are now used to restore existing roof systems by acting as a surfacing that shields the membrane from erosion caused by rain, snow, sleet, and hail. When properly applied, coatings can provide significant advantages to a roof system. Coatings have been documented to extend the service life of existing roofs, improve a building’s energy efficiency, resist degradation from chemical attacks and ultraviolet radiation, and eliminate the formation of small cracks associated with these degenerative conditions.
Coatings also remain important and effective in protecting roof systems from the sun. Coatings, particularly those with reflective and emissive materials, can reduce roof surface temperature by as much as 30 percent and can extend the service life of some membrane systems by reducing expansion and contraction. These cooler roof surfaces lower a building’s interior temperature. This decreases the need for and associated costs of air conditioning and results in less intensive HVAC maintenance over the life of the equipment.
Lasting life
The life of the coating is based on several factors. One is the existing roof condition. Effective coatings work best when applied over properly repaired materials — the coating is only as good as the surface it is applied on. The old analogy of applying paint over an automobile with a bad engine and expecting it to function better is similar to applying a coating to a deteriorated roof system. Improper preparation or repairs of existing roof systems and wet (or saturated) insulation will decrease the coating’s performance capacity. For instance, if improperly repaired blisters split, the coating will also be impacted.
Life span is also determined by the type of coating, thickness, and quality of the application. Most manufacturers provide coating warranties that range from five to 20 years. Consult the manufacturer to determine the best coating for each specific roof area.
It is important to point out that although coatings can extend the service life of the roof system and provide repairs to specific conditions, most coatings do not provide long-term, stand-alone waterproofing protection. Proper roof system (i.e., membrane, insulation, flashings) repairs are required prior to the application of the coating, as the waterproofing is still primarily completed by the existing membrane.
In the past, roof coating applications were typically completed with aluminum coatings. The primary purpose of these coatings was to prevent oxidation and ultraviolet degradation in smooth-surfaced built-up roofs and modified bitumen membranes.
Today, coatings can be applied over all types of low-slope commercial roof membranes and metal. The best surfaces are smooth-surfaced membranes. While application of coatings over aggregate-surfaced membranes is possible, it typically requires the removal of all loose aggregate, which poses challenges.
4 Types of Roof Coatings: How to Pick the Best for Your Facility
There are several types of coatings available on the commercial roofing market. The material formulations, uses, and application methods are all different, so facility managers should examine the manufacturer’s material data sheets to determine which product is suitable for their specific project. Not all coatings are acceptable or compatible on all roof surfaces. Also, all pre-application preparation should be completed in accordance with the roof coating manufacturer’s requirements. As with all liquids and adhesives used in the roofing industry, proper on-site material storage is important, and all of these products have a specified shelf life.
1. Acrylic coatings:
Acrylic coatings were originally developed to provide ultraviolet protection for sprayed urethane foam applications. These types of coatings are now used on a variety of roof membrane surfaces, including single-ply membranes and metal systems. Acrylic-based materials provide excellent resistance to radiation and hail damage and have the inherent flexibility required to withstand the dimensional instability of most roof membrane surfaces. Some studies have indicated that properly formulated acrylic coatings can reduce the surface temperature by as much as 20 degrees F when exposed to direct sunlight at 85 degrees F.
Acrylic coatings are manufactured of 100 percent acrylic and can be applied in one or more coats. Most manufacturers provide warranties based on the coverage rates; extended warranties require additional coverage. Acrylic coatings should not be applied in freezing temperatures or when precipitation may occur within a specified period from the application. The cure time of these products is highly weather-dependent and cold weather or high humidity will impede curing. Ideal curing takes place with warm weather and low humidity.
Acrylic coatings are economical, provide excellent reflectivity, and are easy to work with. These coatings also, however, lose mil-thickness from weathering, require application in an ambient temperature of above 50 degrees F, and cannot withstand ponding water.
Several acrylic coating manufacturers now offer instant-set materials. This reduces the cure time of the acrylic coating to a few minutes, thereby eliminating the possibility of coating run-off if there is precipitation directly after application.
2. Silicone coatings.
Silicone coatings are manufactured with a high solids’ dispersion of 100 percent silicone. It is a highly elastic material that provides excellent adhesion to the existing surface. Silicones provide good weather resistance and rarely become hard or brittle. Silicone coatings have gained market share in the commercial roof market in the last decade. The rise in applications is primarily due to the material’s ability to withstand long-term exposure to ponding water, as most of the other coatings cannot withstand ponding water. Silicone coatings also provide excellent ultraviolet protection in extreme temperatures and harsh environments and can resist oxidation. Silicone is available in a variety of colors and provides high reflectivity and emissivity ratings.
Some of the drawbacks are cost, application requirements, and the fact that there are only a few materials – other than silicone – that can be applied directly to the silicone surface. Silicone also holds dirt on the surface and loses reflectivity over time.
3. Polyurethane coatings.
Polyurethane coatings were initially developed to be applied over sprayed-in-place foam roofs. They are now used as coating applications over a variety of existing roof membranes. Polyurethane coatings provide the best rates of all coatings for impact resistance and for foot traffic. There are two types of polyurethane roof coatings: aromatic and aliphatic. These types of materials are typically used in combination of base coat and topcoat. The base coat material is durable but does not offer high UV resistance. The aliphatic coating is used as a top surface because it is UV stable, stays clean, and holds color longer than other coatings.
4. Fluid-applied asphaltic rubber membrane system.
Technological advances and labor shortages have led to the development of fluid-applied materials that can effectively extend the service life of the existing roof system at an economical rate. An asphaltic rubber membrane system has been developed that can be applied in cold-process fluid-applied applications in use for life extension repairs. The asphaltic rubber material combines the elastic properties of rubber with the waterproof/weatherproof characteristics of a highly refined emulsified asphalt. The resulting formulations are proprietary materials that form a fully adhered monolithic, seamless, rubber membrane. The resulting membrane can be applied to range from 20 mils to 200 mils dry.
Unlike coatings that only provide a film surface or adhesives that require reinforcements for waterproofing capacity, the asphaltic rubber forms a monolithic, seamless membrane that provides instant waterproofing/weatherproofing capabilities. The use of these materials in combination with coatings provides a long-term, economical repair system.
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