ROOF COATINGS Part II- Asphalt & Elastomeric Coatings
Let’s start with asphalt coating. First, NEVER use asphalt coating on an EPDM roof. Asphalt roof coatings have solvents that keep the asphalt in a liquid state. EPDM rubber membrane will be deteriorated by the solvents in the coating. When it comes to roofing there will be two basic types of asphalt coating – Fibered Apshalt Coating and Emulsion Coating. When getting a price for asphalt coating always make sure that it will be fibered asphalt coating. This means it will have fibers mixed into the coating to provide additional strength and help keep it from cracking open.
Fibered Roof Coating may be used on smooth surface BUR, or SBS or APP Modified Bitumen Membranes, metal surfaces and roll-roofing as a protective coating. It may also be used as a restorative or repair, albeit usually a short term one – meaning anywheres from 1 to 5 years. This coating is not resistant to ponding water.
Some contractors or homeowners have used this type of repair for asphalt shingle roofs. ARMA (Asphalt Roofing Manufacturer’s Assoc.) strongly advises against the application of any type of field-applied coating over installed asphalt shingles. Problems reported after asphalt shingle roofs have been field coated include shrinking of the coating, which may result in unsightly curling and/or cupping of the shingles, or loosening of the granule surfacing of the asphalt shingles. In addition, non-permeable roof coatings may create a vapor retarding layer by sealing the voids around and between the shingles. If this occurs, it increases the possibility of rotting of the roof deck caused by moisture accumulation in the attic space.
Most Emulsion Roof Coatings are manufactured with refined asphalt, bentonite clay, emulsifiers and fibers for brush or spray application on smooth surface and metal roofs. The dried film cures to a tough, flexible, durable finish and will resist variations in temperature and weather. Emulsion Roof Coating will not burn or support combustion in a liquid state. It has no odor or fumes,(since there are no solvents) and resists the absorption of exterior moisture. Most Emulsion Roof coating can be applied to slightly damp surfaces and is resistant to ponding water.
Roof repairs using these products are usually done at a coverage rate between 1.5 and 3 gallons of product per roof square. (One square equals 100 square feet) The coating can be applied using spray, roller or brush. Adhesion is best achieved using a roller or brush.
Elastomeric Coatings –
Elastomeric coatings are basically just a rubber membrane in a liquid form.
Some are acrylic based and others have an oil base. The oil based coatings are often resistant to ponding/ standing water while the acrylic ones are not. Some of the advantages are;
-Highly reflective… most of these coatings are white with a high 88% initial reflectivity saves energy costs by directing heat away from the building
-Saves energy… Lowers the temperature inside the building to save energy costs during warm and hot months
-Water based and low VOC… Approved for use even in states with tough UV standards
-Versatile… Can be adhered to a variety of substrates, including granulated BUR, SBS & APP, metal, wood, and concrete and can be applied by spray, roller, or brush
-Strong and resistant… some of these provide up to 150% elongation and 250 psi tensile strength
-Provides a seamless flexible membrane when finished!
Application rates vary depending on the product and, more importantly, the type of surface you are coating. Repairs done with this type of product are a more substantial repair capable of lasting for years.
When this type of product is combined with a reinforcing membrane it forms a roof system. These roof systems may need periodic re-coating.