DEFINITIONS
In the course of communicating Elastek’s waterborne elastomeric roof coating products and their qualities, we often use acronyms and other terminology that bear definition.
Acronyms
AITL — Accredited Independent Testing Laboratory
ANSI — American National Standards Institute
ASTM — American Society for Testing and Materials
CRRC — Cool Roof Rating Council
Terms Defined
Coating Temperature and Aging — The temperature of the coating film at the time of testing has a great effect on tensile strength and elongation. Most published coating specs were measured at around 75º F but at 0ºF elongation drops dramatically and tensile increases dramatically. In essence, elastomeric coatings have “extra” stretch in warm temperatures to assure adequate elongation in cold temperatures. Cold weather issues are not a factor in many Sun Belt locations, but would be in colder climates.
Exposure to solar UV-radiation damages most coating over time, thereby reducing both tensile and elongation. New coatings perform much better than older coatings as a rule. The desert Southwest has exceptionally high levels of UV radiation that damage coating, thus many roof surfaces age more quickly here than in milder climates.
Elongation — When a dry-film sample of elastomeric coating is stretched, as in tensile-strength testing, it deforms or changes shape. By stretching the film in just one direction, the maximum length of the sample at break can be determined with sophisticated equipment. By dividing the stretched film’s length by the original length and multiplying by 100 you get ultimate elongation as a percentage (usually 200% to 400%). At maximum stretch, the film will be permanently deformed. Sometimes “elastic elongation” is noted, which is the greatest percentage of stretch before permanently deforming the film.
Elongation properties are usually balanced with tensile-strength properties to create a coating that has both adequate strength and elongation for a given application.
Heat-Island Effect — This term originated with government labs studying the heating effects of solar radiation. They found an increase of 10º F and more in ambient temperature over urban areas where vegetation and natural landscape had been replaced by numerous buildings, roofs, roads, parking lots, and other structures that absorb or generate heat. The effect is primarily a problem for larger Sunbelt cities, and reflective coatings can be of some help.
Opacity — This refers to a coating’s ability to block damaging solar light from reaching the substrate. Roof coatings use titanium dioxide (and to a lesser degree zinc oxide) to block solar radiation from damaging roofing by reflecting it away from the coating. A coating with good opacity can reduce the amount of coating needed to protect a roof. Opacity is reduced by weathering (erosion) so protective coatings need to be renewed from time to time to maintain protection over the substrate.
Percent Solids — The amount of solid material (non-volatiles such as the plastic particles in resin and mineral powders) in a coating can be determined by weight or by volume, but the significance of these two is often misunderstood. “Volume solids” is the preferable measure, as it emphasizes the level of performance-enhancing resin solids in the coating (coating plastic remaining after the water has evaporated). Because they are 2-to-3 times lighter than mineral fillers, high resin content coatings will weigh less but take up more space in the coating.
A coating with a high level of “solids by weight” may be bad for performance because much of the weight is coming from high levels of cheap powders used to keep product costs down. The level of resin solids is critical because they bind the coating, determine adhesion, elongation, water resistance, and tensile strength. High levels of resin solids are quite expensive and tend to be found in premium coatings. Volume solids will indicate dry-film thickness (multiply wet mil thickness by volume solids as a decimal).
Solar Reflectance — The sun pours vast amounts of energy on the earth every day. Sunlight includes the visible light spectrum and the non-visible light spectrum (ultraviolet and infrared) that composes “solar energy.” Some of this invisible energy can be very damaging to organic materials such as roofs. Other invisible energy can deliver great amounts of heat energy to surfaces. Visible light can also carry some heat energy. By creating roofs and roof coatings that prevent much of this solar energy from entering homes and buildings, these structures stay cooler and the cost of cooling drops significantly.
Solar Reflective Index (SRI) — SRI is an index that incorporates both solar reflectance and emittance into a single value. There is currently disagreement as to whether emittance is nearly as important as reflectivity in keeping roofs cool.
Tensile Strength — Because roof coatings are going to be stretched once in place on a roof, the stretch resistance of the film is important. Tensile strength measures a dry film’s resistance to stretching at the point of breaking. A coating with little stretch may have very high tensile strength but limited elongation, and vice versa. The best situation is usually a film that has a good balance between tensile and elongation (usually 200% to 400% each).
Thermal Emittance — The ability of a material to release absorbed heat, measured on a scale of 0-100, higher being better. As an example, aluminum roof coating has reduced emittance and will hold more heat than a white coating, as anyone on such roofs in the summer would quickly learn.
