Duct tape isn't much good for taping ducts, study finds But don't despair: It's great for car fenders, canoes, shutting alligator mouths


SAN JOSE, Calif. -- Popular wisdom claims you can use it to patch a canoe, repair a dangling fender or keep an alligator's mouth shut. But according to scientists at Lawrence Berkeley National Laboratory, there's one thing duct tape is no good for: taping ducts.

In tests that mimicked conditions in the forlorn and hidden spaces where ducts reside, "what we found was that duct tape almost always failed," said Max Sherman, a physicist who ran the tests. "It failed reliably and often quite catastrophically."

The new study is no laughing matter to energy efficiency experts. They estimate 30 percent of the heat or chill generated in the average home is lost before arriving at a room.

And since most ducts are inaccessible -- hidden in crawl spaces, attics or inside walls and swaddled in insulation -- people rarely notice a key component of their home's circulatory system is failing. This can lead people to replace costly heating or air conditioning equipment unnecessarily.

The impetus for his study was an invention. Colleagues at Sherman's laboratory came up with an aerosol foam that can be sprayed into ducts to seal leaks, then developed tests to see if it worked. They have since formed a company, Aeroseal Inc., to market the stuff.

They tested duct tape. By definition, it combines a rubber adhesive with a fabric backing. Although the classic version is silver, it also comes in an array of colors and in a number of grades, from economy to professional and even nuclear.

The lab also tested other tapes used to repair ducts: gooey black tapes, clear acrylic ones and foil-backed ones. The scientists also tested the aerosol foam that had been invented at the lab and mastic, an adhesive that's glopped on like glue and left to dry. All are supposed to withstand the 200-degree temperatures encountered in heating systems.

The researchers applied each sealant to gaps on pieces of sheet-metal ducting. They baked the ducts to simulate conditions in a hot attic and blew air through them at temperatures ranging from sub-freezing to 180 degrees.

"We assumed we would get a whole spectrum of failure. There would be good products, bad products, products in the middle," Sherman said. "Duct tape tended to fail very quickly -- in as little as three days in our testing system to as long as two months."

At a meeting of energy efficiency experts in Monterey, Calif., this week, Sherman and his colleague, Iain Walker, passed out pieces of duct tape that had been through the tests.

"You can see with a lot of these failed tapes there is a lot of shrinking, drying and separating," Sherman said. "Some are dried to a crackly crunch."

Of the two dozen people at the session, nearly half said they had found duct tape that had lost its usefulness while inspecting homes.

Based on many such reports from the field, the California Energy Commission is now considering new standards that would require homebuilders to use something other than duct tape in heating and cooling systems if they want to get credits for saving energy, according to Scott W. Matthews, the commission's deputy director for energy efficiency.

The lone representative of a duct tape manufacturer at the meeting was Jerry M. Serra, vice president for research and development for Kendall Polyken in Massachusetts.

"I can honestly say I have not had one field failure come back to my laboratory," he said. "Maybe they're just not complaining, I don't know. But whatever it is, we want to make a product that works."

Matthews noted the Berkeley results have not been duplicated in other laboratories: "You should have more than one test that shows something before you reach scientific conclusions."

Pub Date: 8/27/98

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