Most roofs benefit from a protective coating provided that they are applied before so much damage has been done that the roof life can not economically be extended. It is not unusual for isolated areas to be replaced, which is more economical when full roof replacement isn’t necessary. Some areas of roof weather harder than others.

Roof coatings come in three forms based upon how they cure; mixed with water (waterborne), mixed with a different solvent (solvent based), or a catalyst (parts mixed together react and result in curing). The 1st two cure by evaporation. Catalyst coatings are less popular due to material and application costs.

Asphalt coatings typically have the least initial cost and are applied for a variety of reasons. They are more temporary and can be applied in areas without doing an entire roof since they do not require a continuous film.  They are more vulnerable to UV and weather and require more frequent application. Asphalts are blended for either higher or lower melt temperatures. One resists hot temperatures without flowing. The other resists cold temperatures without becoming brittle. They are either black or pigmented with aluminum and produce minimal to no temperature reduction.

Elastomeric coatings (coatings that stretch) have become most popular because of their greater durability and energy savings since they can be made in a full range of colors including bright white. These are longer lasting provided that they are formulated properly. Having “100% acrylic” or “rubberlike qualities” does not tell whether the ingredients are the most suitable for your application or even of great volume in the product. Physical properties will, however, compare for you what you are getting and can give you a reasonable prediction of relative performance. Elongation and tensile strength are the primary features elastomerics are purchased for. They are available in white and a variety of colors, making them popular for aesthetics and temperature reduction. Elastomerics will perform over a wider variety of temperature conditions. The quality of UV resistance is essential.

Water based elastomeric coatings are best used over breathing porous surfaces such as stucco, block, concrete walls, and certain polyurethane foam roofs. They have an open particle structure that allows vapor to dissipate. They are characterized by a high “perm” number. For this reason there are better answers for substrates such as metal that is subject to corrosion, roofs that tend to pond water after precipitation (invades the voids within the coating structure resulting in failure), and some felt roofs. Water based coatings are vulnerable to wash off from rain or heavy dew, and freeze damage before curing. Consequently their use should be guarded in spring or late fall when freezes occur. The water based coatings “chalk off” faster then their non-water containing alternatives do but provide for easier applicator clean up.  Water contained in water based products can trigger flash rust, and the larger particle sizes that allow moisture migration also hinder effective rust prevention

Non-water based (petroleum based solvent or catalyst cure type) elastomeric coatings are best used over surfaces that do not need to breathe moisture (metal, dry substrates, rubber modified bitumen, etc.). There are only a few manufacturers capable of producing these due to the technology and investment required. These coatings have an extremely low perm rating that act as a vapor barrier and result in a superior seal. Consequently they are tight and often offer superior physical properties. They are preferred for extending application seasons. Using these type products is not recommended when a damp substrate exists (caution to not apply any coating over any damp substrate per NRCA and most manufacturer requirements). This can result in problems of concealed damages, coating blisters or delimitation between the substrate and coating.

Some manufactures supply a variety of coating types. A simple rule of thumb applies here to evaluating them. Ask for certified independent laboratory results that compare their product to established standards and even competitive type products of others. Then compare the physical properties. These are what stay with the property long after the work is performed. Independent reports provide you greater assurances of the properties and seriousness of the supplier. Product capability is not an area to be pennywise and pound-foolish.