From a building code perspective, a coating can be applied on new and existing roofs as a maintenance item; application of a roof coating is not considered to be the application
of a new roof. Therefore, an existing roof can be coated or re-coated at any time—for example, a building owner can add a highly reflective roof coating to reduce energy costs. Additionally, applicators of a roof coating on an existing roof should consider any in-place warranties so they are not voided or violated.
The 2015 IBC lists acrylic, silicone, and moisture-cured polyurethane coatings for use on SPF roofs. Each has an ASTM material standard that each type of coating must meet.
- ASTM D 6083-05e01, Standard Specification for Liquid-applied Acrylic Coating Used in Roofing;
- ASTM D 6694-08, Standard Specification for Liquid-applied Silicone Coating Used in Spray Polyurethane Foam Roofing Systems; and
- ASTM D 6947-07, Standard Specification for Liquid-applied Moisture-cured Polyurethane Coating Used in Spray Polyurethane Foam Roofing System.
Figure 1 lists film physical property requirements for each coating type.
To date, there are numerous coating types that do not have consensus standards (e.g. ASTM) for minimum properties. Specifying coatings that do not have a consensus standard should be based on physical properties provided by manufacturers. Some of the coating types that do not have an associated ASTM standard include polyureas, aliphatic polyurethanes, aromatic urethanes, butyl, and SEBS coatings.
Application considerations
Coating application includes considerations such as;
- storage;
- surface and substrate preparation;
- primer use;
- application specifics; and
- curing and drying time.
Storage
One should always keep roof coatings stored as close as possible to room temperature. In cold weather, a heated warehouse is generally the preferred type of storage area. Water-based products susceptible to freezing may be damaged or rendered useless if subject to temperatures at or below 0 C (32 F).
Surface and substrate preparation
The roof must be thoroughly cleaned, and allowed to dry completely. This is a critical step to ensure a successful coating application. Dust, chalking film, bitumen exudate, grease, oil, and other loose debris should be cleaned off the roof surface before the coating application. Care should be taken when pressure-washing to not disturb the integrity of the underlying roof membrane, particularly where there are adhered seams. Roof coatings should never be applied to a frost-, snow-, or ice-covered surface. In addition, for most solvent-based roof coatings, the surface must be dry unless the coating has been specifically formulated for adhesion to wet surfaces. It is advisable to apply coatings only when there is a minimum of 24 hours before forecasted rain. Coating manufacturers have specific requirements for roof preparation.
Primer use
Primers are designed to prepare the roof surface for accepting a coating and improving the overall adhesion. However, a primer is never a substitute for proper surface preparation. Typically, these products exhibit low viscosity and are formulated to quickly wet the substrate in a thin layer. When cured, it will leave behind a thin film acceptable for receiving a coating. Primers are available in various binder and solvent combinations, and the type used in a particular application will be based on the substrate, weather conditions, and coating type.
Any required roof or flashing repairs should be completed and allowed to adequately cure as necessary. Some water-based primers may be applied to damp, but not wet, surfaces. Coating manufacturers can be consulted about non-dry surface application. Applying the surface coating should occur soon after the primer has been spread and cured to ensure the desired results.
Surfaces that generally require primer include metal flashings, gravel stops, and other metal edging. Certain roof substrates may require priming not only to promote adhesion, but also to prevent the substrate from negatively impacting the coating performance. For example, rust-inhibitive primers are often used to prevent rust/corrosion on metal flashings from transferring through to the surface of a water-based coating.
I’m surprised that I have never heard of roof coatings, especially since they have been around for 50 years! The shingles have been falling off of my roof lately, so I need to get it fixed soon. If I coat the roof after replacing the shingles, will it last longer?
This was a lot of help! I wasn’t sure which coating I should go with for my new roof so this is great. Thanks so much for sharing.
Some great info about the different roof coatings!
It is interesting to see how many different type roof coatings there is. We have been using acrylic roof coatings for years, may have to look other options now!
I want to get something that will make my roof last longer. It makes sense that I would want to have it coated! It seems like a good way to keep it safe from the elements.
Informative post shared about the different roof coatings. I was doing a little survey on types of roofs done these days. Thanks so much for sharing.
Roof coatings is an effective way to restore flat, low sloped, EPDM and metal roofs – but almost every roof can benefit from reflective roof coating, whether acrylic or rubber.
Thanks for sharing! It’s awesome how you mentioned about such an option which protects and extends the service life of the roof. My wife wants to prepare our roof for the autumn with its rains, and as I’m not a handyman we need professional roofing services. So’ll definitely consider these recommendations in order to protect our house to the greatest degree.
I had no idea there were so many options for roof coating. Ive been racking my brain trying to figure out what Im going to do. I live in tucson where roof coating is super important as the sun and monsoons are especially brutal. This article: http://bluecoyotepainting.com/tucson-roof-coating-what-to-know/ says I should be doing it every 5 years or so. Im hoping the right coating can last longer than that.
It did catch my attention when you talked about how asphalt coatings are a perfect choice for roof coating if you want your roof to be protected from the cold and inclement weather. My father is interested in roof coatings to extend the life of our roof. We know how extreme weather conditions can affect the lifespan of our roof, so it’s important for us to choose a roof coating that can protect our roof from harsh weather conditions.
On old, weathered asphalt roofs, many coating manufacturers recommend use of an asphalt primer after cleaning the membrane to prepare the surface for coating. Primers for metal roofs A number of different types of factory-finished, metal roof panels are available. EPDM Roof Coatings is good for roof strength in long term.
Finding a good contractor can be difficult because there are so many different ones out there. I really like the idea of asking your family and friends about who is good to to hire.