Get the Scoop on Asphalt Shingle Coating

Photo: click/morguefile.comYou may have seen advertisements for roof sealants designed to be applied directly to asphalt roofs. Such sealants are supposed to stop leaks, extend the life of your roof, and prevent the growth of mold and mildew. Another type of sealant for asphalt roofs is a white reflecting coating designed to help keep homes cooler in hot and tropical climates, where a dark roof can hold heat and make the interior unpleasantly warm during the day.

What's the skinny on these products? What exactly are they, how do they work, and more to the point, do they work at all? Are they a good choice for your roof?

Roof Sealants -- Purpose

Let's talk about sealants first. These products are made from an acrylic that can be sprayed or rolled onto a clean roof. While it goes on white, it dries to a clear finish so the existing shingle can be seen underneath. The stated purpose of a sealant is to extend the roof's life by protecting the shingles, and while manufacturers don't offer a guarantee on wind damage, many claim that sealants can help prevent shingles being torn off by storms.

Problems with Sealants

However, there are several problems with sealants. The first is the actual preparation of the roof. Although pressure washing is sometimes recommended to get the roof as clean as possible before the sealant application, professional roofers actually advise against pressure washing roofs because this can damage the shingles. Furthermore, a sealant isn't going to fix an already badly leaking and damaged roof; the only repair for that is an actual roof replacement.

Using a sealant may extend the life of a roof by a few years, but roofers note manufacturers' claims that sealants add 10 or more years aren't supported by what they see on the job. At best, sealants can be a stopgap measure to keep a roof going for a few more years. And sometimes they can even damage a roof. One big concern is that a coat of sealant could disrupt the natural permeability of the roof, meaning it won't ever get a chance to fully dry out, which could lead to condensation inside the roof as well as the attic. That's bad news for joists and other structural components of the roof!

Roofing professional Maciek Rupar details a number of the problems with applying sealant coatings to asphalt roofs, illustrating that many roofers are leery of these coatings. Furthermore, so are home inspectors, who haven't been satisfied with the performance of the sealed roofs they've inspected. While sealants are suited for use on low-slope roofs designed for them, they might not be a great choice for asphalt roofing on a medium to high slope.

Coatings to Create Cool Roofs?

In terms of cool roofs, it's tempting to apply a coat of white paint to a roof to bring down the temperature in the summer. A cool roof can cut energy use dramatically and make a home more comfortable, but unfortunately, converting an asphalt roof may not be as simple as applying a coat of white sealant.

The roof needs to be clean and in good condition before any attempt at applying a coating, and it's possible that the coating may not adhere evenly. Experts at Dow Chemical, one manufacturer of such coatings, note that they can actually cause leaks, as the edges of shingles may turn up and create an opening for water. There's also a risk the coating won't adhere to the asphalt, unless it's specifically made for asphalt roofs, so it's critical to make sure you use the right product.

Consult a Roofer

While sealants aren't universally a bad idea, you should definitely consider carefully before applying them. Consult a reliable roofer about your options, and get an estimate on several different approaches to the issue you're trying to resolve. If, for example, your roof is heavily worn and you'd like to get a few more years out of it, your roofer may have some bad news for you: it could be time for replacement. On the other hand, when you have a fairly new roof in good condition, a sealant might be a good choice.

Sealant technology and roofing technology are both in a constant state of evolution. As the roofing industry adjusts to the entry of sealants into the market, it's also working with manufacturers to develop products that work well with a variety of roofing types. Make sure your roofer knows about the latest trends in the industry to ensure that you get an accurate and honest appraisal of the situation from someone who's familiar with all the available options, their risks, and their benefits.

Get Multiple Quotes

And don't be afraid to get quotes from a couple of different roofers to gain a complete understanding of the picture. You may discover that there are significant differences in estimated price as well as options for the job. Find out why some roofers advise against coating and if a roofer offers an unusually high or low bid, press for details. Anything involving your roof is a big decision, because it's a key (and very large) component of your house. Take the time to ensure you make a wise decision.

Katie Marks writes for

Updated February 6, 2018.

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