Two Types of Reflective Coatings Address Different Needs
Here's a look at the basics of coatings that reflect heat and light.
The most common types of reflective coatings are those used to reflect heat and light, and both kinds can be used for interior and exterior applications. These coatings are usually marketed by specialty paint and coating manufacturers.
- Heat-reflective coatings are usually high performance coatings such as PVDF or an acrylic. These are primarily used to reflect heat from a structure or assembly such as wall or roof, with roofs being the most common application. The first heat-reflective coatings were bright white and had to be kept clean to maintain reflectance.
Another type of heat-reflective coating uses reflective particles, such as aluminum or ceramic; these particles are blended with the coating during manufacture. Alternatively, a heat-reflective powder is blended with the coating by the applicator just prior to application; the additive is normally added to the finish coat.
Heat-reflective coatings can be applied to most substrates, such as drywall, plaster, metal, masonry, etc., where a thermal barrier is desired. When used on the exterior, the product data sheets should be checked for resistance to UV and humidity; if used on metal, for flexibility; and if used in coastal locations, for salt-spray resistance.
Roofs are probably the most common substrate coated with heat-reflective coatings, and the coatings can be applied to most any type of roof surfaces, including metal, built-up, modified bitumen, and TPO. The main benefits of heat-reflective coatings are reducing surface and interior temperatures and extending roof longevity.
Reflective powder additives can be heavy enough to settle to the bottom of paint containers after being added. However, mechanical or manual agitating prior to and during application will keep the additive uniformly distributed to provide a more even distribution and application. Heat-reflective coatings can be applied in a 2-coat application by brush, roller, or spray. When spraying heat-reflective coatings, follow the manufacturers’ application instructions to ensure additives flow more freely and evenly through the sprayer. The additives may alter sheen and colors of undercoats. Therefore, a mock-up of the intended coating is recommended especially if aesthetics are important. Reflective additives may increase wet-film thickness during application, which may increase curing time.
- Light-reflective coatings are sometimes referred to as retro-reflective coatings because they reflect light back to its source. These coatings use reflected light to mark a boundary such as outlining machinery or equipment and to indicate highway markings. The reflection is achieved by small glass beads added to a colored base coating that is usually white or yellow. These beads are typically round and transparent which allows light to hit the beads and then be reflected back to the light source. Since reflective coatings do not require a power source other than transmitted light, they are ideal for remote locations.
Another type of light-reflective coating uses color to achieve reflectance. Some coating colors are more reflective than others and are used to make an entire surface, such as a wall, be reflective. These coatings are marketed by some trade sales paint manufacturers. The effectiveness of these coating is usually measured as a percentage of the amount of light they reflect. This percentage is called Light Reflectance Value (LRV), which is measured on a scale from 0 to 100 percent. A color with an LRV of 0 percent means all of the light is absorbed and none reflected. An LRV of 100 percent means all light is reflected and none absorbed. An absolute black, if it exists, would have an LRV of 0 percent and would allow surfaces to be warmer compared to colors with a higher LRV. Pure white, if it exists, would have an LRV of 100 percent, meaning all of the light is reflected, which would allow surfaces to remain cooler than colors with a lower LRV. Theoretically, all colors will fall between 0 and 100 percent, and coating manufacturers can provide actual values for a particular color.
Independent testing suggests that colors with higher LRV can last longer because they reflect more heat and UV, which are properties that are detrimental to the coatings. However, absolute black or perfect white are not available. Testing by independent testing facilities show that the lowest LRV is approximately 5 percent (a black), and the highest is approximately 85 percent (a white).