When Air Management Industries was hired to seal ductwork on a government-owned building in downtown Los Angeles, officials knew standard brush-on sealant wasn’t going to cut it.

The exposed, rooftop duct had been coated before. The Southern California sun was more than its match.

“It had been sealed with typical brush-on many, many, many times and it didn’t last year long,” said April Yungen, owner of Rancho Cucamonga, California-based AMI.

She decided that another product was needed to protect the duct. She chose rolled mastic sealant from Hardcast HVAC.

It’s a decision that many HVAC construction and duct sealing contractors today are making, according to officials with Hardcast, which makes and markets numerous duct sealing products — both liquids and mastics — under the Hardcast name. The choice to use rolled mastic sealant is also being driven by code officials in much of the country, where regulations are mandating either UL Class 0 or 1 or UL-listed products in HVAC systems.

A rolled mastic sealant is much more than a tape, said Tim Eorgan, Hardcast’s Specified Products Manager. Most HVAC tapes are only 3 to 5 mils thick. Rolled mastic sealants are going to be at least 17 mils thick.

“You don’t want to call it tape,” Eorgan said. “You’ve got to say ‘rolled mastic sealants’ because that’s how the code is written in some states.”

When compared with the more common brush-on liquid sealants, rolled mastics offer several advantages, Eorgan said. They don’t give off any irritating gases or volatile organic compounds, making them more pleasant for workers to apply. He pointed out Hardcast’s are the only truly zero VOC products on the market.

“Even the ones that say they’re zero VOC, they all give off some gases,” he said. Some even contain acetone, a strong-smelling ingredient in many nail polishes and a possible fire hazard.

Brush-on sealants shrink as they dry, reducing the protection they offer. You have to allow time for the product to dry before you can move it, wrap the ductwork or even test the HVAC system, Eorgan added; that slows worker efficiency.

“With a liquid-applied duct sealant, you’re going to have to wait 24 hours to turn the system on,” he said. With rolled mastic sealant, a system can be started up almost immediately.

It’s especially important in applications where contractors are choosing to wrap ductwork after sealing it — a growing trend, Hardcast officials said. Such approach offers extra protection, and in the case of Hardcast products, a 10-year warranty is available on the Hardcast Foil/Sealant Duct Sealing System.

“You can’t wrap ductwork when there’s a liquid drying on it because it creates a mess and you will destroy the seal,” Eorgan said. “But if there’s a rolled mastic sealant, you put that on and it’s already dry. You can start wrapping your insulation around it. You don’t have to wait for it to dry because there’s no drying time.”

That’s the multistep approach Air Management Industries picked when it came to the rooftop L.A. building, Yungen said. After applying the liquid sealant, they applied the rolled mastic. Despite triple-digit temperatures, the project went smoothly. 

“It was about 105 (degrees) when we were doing this job,” she said. “It couldn’t have been a worse time of year. It went on well. The rolled mastic sticks great.”

Eorgan said he’s not surprised by the excellent adhesion.

“It’s a beautiful system for outside, because outside you’re subject to rain, you’re subjected to chemicals, ponding water, and the worst thing — you’re subjected to sunlight,” he said. “And with that rolled mastic sealant, with that mils of foil being on top of it, sun and water is not going to harm it.”

And AMI discovered Hardcast’s rolled mastic sealant works indoors, too.

 “We also use it inside (buildings) for a quick fix of a hole that the brush-on just wouldn’t coat,” Yungen said.

 While Hardcast still manufacturers and markets traditional brushed-on sealants, more contractors are expressing a preference for the company’s Foil-Grip line of rolled mastics, Eorgan said. They cost a little more than the liquid versions, but the time and labor savings from using the rolled mastics more than make up for it. It’s especially popular among building contractors who perform residential new construction work.

“It’s not going to let air out or water come in,” he said.