Building Operating Management

Solvent-based, Water-based Roof Coatings Have Pros And Cons





Roof coatings can be roughly divided into solvent-based and water-based varieties. Solvent-based coatings, such as urethanes and silicones, tend to last longer, but can be more expensive and require greater care in their application. Water-based coatings generally emit fewer odors (one reason hospitals and universities often prefer them, Ripps says) and cost less, but may not last as long.

One type of water-based roof coating, acrylic, accounts for a large segment of the market. Many acrylic coatings are both white and reflective, says Tom Meyer, technical liaison with Coating & Foam Solutions and secretary/treasurer of RCMA. They also tend to be lower cost than many other coating products, he adds. However, these coatings may run if it rains before they've dried, and typically shouldn't be applied in colder weather.

Acrylic coatings tend to be popular in the southwestern and western states, says Steve Heinje, technical service manager with Quest Construction Products. "From the Rocky Mountains to the Cascade Mountains is good acrylic territory."

One interesting acrylic application actually comes from Miami. The 605 Lincoln Road building, built in 1932, needed to maintain a watertight roofing system, as the top floor housed a data center. At the same time, the roof also was used as a deck, so any coating had to withstand foot traffic. Workers first applied a water-based acrylic system. On top of this, they applied two coats of an abrasion-resistant coating designed for high traffic areas like decks and roof walking areas. This coating was applied in alternative waves of blue and white. As a result, the roof really doesn't look like a roof.

Aluminized asphalt roof coatings can be found in both solvent- and water-based mixtures, and can add both reflectivity and protection, Heinje says.

These coatings often make financial sense in cooler regions of the country. "Aluminum pigmented coatings and light gray colored coatings both repel heat and hold warmth," Ripps says. As a result, they can be optimal in climates that have more heating days than cooling days.

Silicone coatings also come in solvent- and non-solvent versions, Meyer says. Because of their inorganic chemical makeup, they can be some of the longest lasting roof coatings, he adds. Moreover, many can be applied in colder weather, although they may take longer to cure.

That's not to suggest silicone has no shortcomings. "The Achilles heel? These are soft, like silicone spatulas," Meyer adds. That makes them less suitable for roofs that have to handle a great deal of foot traffic or maintenance work.

Heinje says he's noticed a resurgence in the market for silicone coatings as a result of the safety and easy application of newer silicone products. While the initial costs can be higher than they are for other coatings, these products often hold up well, which can lower the total life-cycle costs.

And because silicone coatings can resist water just hours after being applied, they tend to be popular in areas that receive more rain, including Florida and the southern half of the Midwest, Heinje adds.

Urethane coatings, which generally are solvent-based, also tend to be higher in tensile strength. As a result, the coatings are both tough and flexible and resist abrasions, due to urethane's "molecular spring," Heinje says.

But because they're solvent-based, urethane coatings can emit odor during application, and may be more expensive than some other options. And they may be flammable, requiring special transport and storage accommodations, Heinje adds. But urethanes also have the reputation of being durable.

Both silicone and urethane coatings tend to be more expensive than other types of coatings, Ripps adds.

Once a coating is in place, the maintenance is fairly straightforward. Ripps says he recommends checking the roof twice a year and clearing off any debris that could damage the roof or coating.




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  posted on 10/30/2013   Article Use Policy

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