When the 27-year-old Masonite exterior of her two-story Colonial house began visibly decaying last year, Vienna resident Dagmar Cosby explored her options. The commercial artist wanted a low-maintenance solution, but objected to vinyl siding for aesthetic reasons.

In September 2003, she found her answer -- a product generically known as liquid siding, a specialty paint that makes head-turning claims about durability.

Liquid siding, introduced into U.S. markets in 1996, is also sold as liquid vinyl siding, spray-on siding and architectural ceramic coating. This "permanent coating system," which is sold by established contractors and by overnight start-ups, is generally warranted not to chip, flake or peel. It also is said to resist dirt, fading and mildew; make homes waterproof yet breathable; and possibly reduce utility bills. Typically, it carries a 25-year "paint and forget" warranty.

Cosby, 59, is a satisfied customer. "They did an absolutely fantastic job," she said. "Even the doubters said, 'Wow, it really is nice work.' " As part of its $17,000 contract with her, Procraft of Virginia even swapped out her bad Masonite with new.

But some experts in the paint industry and academia are skeptical and call for more rigorous testing, especially given the generally uneven track record of aftermarket service providers. They also point to a recent controversy in Tennessee, where dozens of complaints of shoddy workmanship eventually prompted the Knoxville Procraft franchise to close. Many of the franchise's customers are saddled with huge bills, peeling "space age" paint and toothless warranties.

On June 18, 2002, the Federal Trade Commission barred the liquid siding industry from making further claims that a thin coating could insulate as well as six to seven inches of fiberglass batting.

Harry Williams, technical services manager at MAB Paints in Broomall, Pa., is among those with reservations about liquid siding. "There aren't a lot of secrets in this business," he said. "If something out there is working head and shoulders above what's common in the business, everybody would be into that particular formulation of chemistry." Notably, Consumer Reports recently top-rated MAB's exterior paint.

Some may have doubts about liquid siding, but not Greg Deathridge.

Owner of five Procraft franchises -- four in Virginia, one in Florida -- Deathridge said he has coated more than 2,000 properties in the Old Dominion since his business launch in 2000. Noting that the typical job runs $10,000 to $12,000 nationally, he said his crews recently put the finishing touches on a $66,000 project in Fairfax County.

"We're about three to four times the cost of a premium paint job," he said. "You can't stay in this business if you're not doing really good work. Our buyers are people who would never put up vinyl siding. These are people in historic areas that love the look of fresh paint."

Though content with Procraft's workmanship, customer Cosby tempers her enthusiasm, acknowledging that even conventional paints typically show no problems just one year after application.

Janice Ozolek of Williamsburg said she and her husband are similarly satisfied -- and cautiously optimistic. Four years ago, the couple paid Deathridge about $20,000 to coat their cedar-faced house.

"We've been pleased with the product," she said. "But the jury is still out."

So new is liquid siding, in fact, that neighborhood associations and historic districts are responding to homeowner inquiries about using the product, with little independent testing to guide them.

The national chain of Procraft dealerships make it an industry leader, but competition and proprietary formulations abound. Typically water based, most brands have large concentrations of vinyl or latex solids. A five-gallon bucket of Deathridge's product, called the Original Liquid Siding, weighs 60 pounds. It is sprayed on in three layers: sealer, thermal blanket and tinted top coat. When dry, it is credit-card thick.

"We cringe when people call it a paint," Deathridge said. "It's a coating, which is considerably thicker. We know that thickness equates to longevity."

Liquid Siding of America, based in Bellingham, Wash., makes the coating for all Procraft franchises. According to Deathridge, his crews can apply it to any exterior except vinyl and glass.

In recent years, manufacturers of consumer paints have slowly ventured into the risky realm of long-term warranties. Olympic's premium exterior latex paint, retailing at $15.98 per gallon at Lowe's, boasts a 25-year satisfaction guarantee, labor costs excluded.

Paint chemists and other experts note that any paint's durability depends on its application. Bad surface preparation invites water infiltration and premature failure. Deathridge said his crews caulk every seam, joint and crack on a customer's home. The goal, he said, is to "build a continuous membrane, so there's no way for water to penetrate."

Describing liquid siding as "good science," he decried both the Tennessee uproar ("bad management") and overheated sales pitches by rogue businesses. He said he has pushed for self-policing within the industry. Records from Virginia's Better Business Bureau Web site show a satisfactory record among his Virginia franchises.

Noting liquid siding's extraordinary claims, a small but growing number of researchers, architects and paint experts is demanding evidence.

Richard Boser, head of the department of technology at Illinois State University, has given presentations on liquid siding. His conclusion is mixed. "We found a great deal of difficulty getting straight answers from the manufacturers," he said. "In every one of those [problematic Tennessee] cases, we found it involved putting [liquid siding] over wood." According to Boser, wood's significant expansion and contraction make paint more susceptible to cracking, bubbling and peeling -- the very issues that have bedeviled the Volunteer State. But he also said the technology has its merits. "Some of those beautiful old Painted Lady houses in Cape May have [liquid siding] on it," he said.

Andre Desjarlais, a researcher in the buildings technology center at Oak Ridge National Laboratory, objects to the industry's testing claims. One key test, he said, bore a significant mathematical error that overestimated insulation value by a factor of 1,000. And another test, he said, "was kind of the equivalent of a grammar-school science experiment."

He also discounted claims that the "world's leading test laboratories" have subjected liquid siding to scientific examination. "At least within the energy efficiency arena," he said, the labs cited "are not anywhere near world-class."

Paul Guevin, a coatings chemist in Columbus, Ohio, is also unconvinced. "It's a lot of marketing mumbo jumbo," he said. "The proof is in how well it lasts 15 to 20 years from now, not in two or three" years.

Jeff McElroy, owner of Bearden Decorating Center in Knoxville, the center of consumer discontent with liquid siding, also weighed in. "A good typical exterior paint job should last seven to 10 years," he said. "If you pay five times as much for something that's supposed to last 25 years, it's still not a good deal." Some customers have asked for his advice on how to remove defective liquid siding. Such work, he tells them, may entail the use of chemical strippers.

There are a number of regulatory, scientific and consumer groups that have no knowledge of liquid siding. For instance, the NAHB Research Center in Upper Marlboro, a subsidiary of the National Association of Home Builders, has little information on the product. Same story at ASTM International where, despite its paint and plastic subcommittees, it has developed no knowledge base on liquid siding. At Consumer Reports, meanwhile, a spokesman said liquid siding has never appeared on its radar.

But liquid siding has appeared on John Evans's radar and he said he's a satisfied customer. Evans, president of Suffolk-based Creative Custom Homes of Virginia, recently spent "into the upper teens" to coat the trim on a $2 million Williamsburg-style house in the Virginia Tidewater. He hopes this low-maintenance option will help sell future homes.

"We've got a product that's been on for less than a year," he said. "Performance-wise, at this point, I've got to say, it's great. But the story will be down the road."