The Fine Art of Foam

Mike Wiltshire, dragging a bundle of hoses across a sweltering roof, explains some basics: Move smoothly, maintain your equipment; a heavy wind is your worst enemy.

He is enveloped in a paper-thin safety suit, dark glasses, a baseball hat and crusty tennis shoes wrapped in duct tape. The outside temperature is approaching 100 degrees.

He lowers his spray gun into firing position and squeezes the trigger. A chemical batter hisses out, rising like a pancake on a hot skillet when it hits the roof.

It’s not complicated, but it can take years to learn how to put down an even coat of foam.

“You have to be careful,” warns Wiltshire, 47.

Rocket scientists concur.

Spray-on foam is the main reason that NASA has indefinitely grounded the space shuttle fleet. The insulating material keeps coming off the shuttles’ massive external fuel tanks.

A 1.6-pound chunk damaged the shuttle Columbia’s wing during liftoff in 2003, leading to the spacecraft’s destruction as it reentered Earth’s atmosphere 16 days later. Another piece came off during Discovery’s launch July 26 but did not strike the spacecraft.

Despite spending $1.4 billion since the Columbia accident to make the shuttle safer, NASA scientists have not resolved the foam problem.

Long before spray-on foam became a Space Age material, it was used on planet Earth to make boats float, keep hot tubs hot and insulate oil tanks, walls and roofs. The simplest version, for do-it-yourself crack filling, comes in a 16-ounce can available at Home Depot for $4.97 plus tax.

Foam on the shuttle tank “isn’t fundamentally different from what you spray in the wall of your house,” says Sidney Perkowitz, a physics professor at Emory University in Atlanta and author of “Universal Foam: Exploring the Science of Nature’s Most Mysterious Substance.”

Wiltshire has never worked on the space shuttle, but he has sprayed a few thousand roofs. He’s happy to guarantee his work for 10 years. But doing it right, that’s the catch.

“Foam is tough stuff,” he says, “but it is a little bit finicky.”

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Atop Goddard Middle School in Glendora, Wiltshire lurches backward, spraying his foam gun left and right over the flat rooftop.

The gun is hooked to two bundled hoses that sit on his shoulder like a boa constrictor. The lines wind behind his back, across the roof and down one story to two chemical tanks in his truck.

Line A carries a chemical compound known as a diisocyanate. Line B contains a chemical mix whose main component is a polyol.

A and B merge at the tip of Wiltshire’s gun.

A hot reaction starts immediately.

Wiltshire says a classic foamer’s prank is to squirt a dollop of the mixture into somebody’s back pocket and watch him drop his pants.

He can spray a strip about 4 feet wide in one pass. A good applicator can lay down a 1-inch coat as smooth as a milkshake.

In less than a minute, the foam is strong enough to walk on. You can carve it with a knife, but it’s flexible enough to dent slightly with a hard press of the thumb.

There are plenty of ways to mess up a foam job.

You can’t spray in the rain or when the temperature dips below 65 degrees. A drop or two of sweat can cause a blister on the surface, Wiltshire warns.

Applied in tight spaces, expanding foam can break a plaster wall. If the chemicals are contaminated or the pumps malfunction, the foam may never cure and instead remain a gooey blanket.

A smooth, clean job depends on the skill of the sprayer. You can train a decent foamer, but experts say the best ones are born with the talent.

“You move to a certain rhythm,” says Mason Knowles, executive director of the Spray Polyurethane Foam Alliance, an industry group in Fairfax, Va. “People who are good dancers are good applicators.”

NASA has taken the craft of foaming to new technological heights.

The shuttle tank is a foam job like no other. The insulation prevents ice from building up on the outside of the frigid external tank -- falling ice could strike the shuttle and damage its insulating tiles.

It also shields the fuel from extreme heat as the spacecraft accelerates. Some parts of the tank hit 1,200 degrees.

The 154-foot-long tank is actually three cylinders stacked end-to-end. The rear tank holds liquid hydrogen at 423 degrees below zero. The top tank contains liquid oxygen at minus 297 degrees. Between them is the “intertank.”

Each tank is upended and foamed individually. Temperature and humidity are carefully controlled.

A computerized spray gun inches up as the tank is slowly rotated. The foam goes on in overlapping spiral stripes, like a barbershop pole. It is a third of an inch thick, on average.

The robotic sprayer can insulate only the smooth body of the tank. The struts, ducts and ramps that protrude must be foamed the old-fashioned way: by hand, using a polyurethane mix that is virtually identical to that used on roofs.

Foam has primarily come off from those irregular spots, NASA says.

Roofers are not surprised. Wiltshire points out the metal strips that form the edge of the school roof in Glendora.

“Sometimes the foam will crack at the places where the metal overlaps,” he says. “It is not a perfected science.”

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The craft of foaming owes its existence to an accidental discovery.

In 1937, a young chemist at the German company Bayer was experimenting with solid plastics when some acid dribbled into a reaction. The scientist, Otto Bayer, who was unrelated to the founders of the company, noticed that carbon dioxide bubbled off. The material was filled with tiny holes.

It was the first polyurethane foam, according to a company history.

His bosses were unimpressed. “At best, a material for making imitation Emmentaler cheese,” they noted in a 1941 laboratory report.

Foam had a grander destiny.

Bayer and his team eventually learned how to tweak the basic chemical reaction to make foam rigid or squishy, dense or airy.

One early formulation was used to strengthen airplane wings. In 1948, the company helped create a twin-walled beer barrel insulated with foam.

The new material eventually became a major component in sofa cushions and car dashboards.

The earliest plastic foams were created by pouring their liquid components together in a mold.

By the 1960s, it was possible to spray on foam, making it a convenient way to insulate tanks, meat lockers and roofs.

Mike Wiltshire came to the world of foam by accident, too.

He was a teenager when his father, Dave, quit his job as an aerospace worker to capitalize on this futuristic insulation. His father insulated roofs, potato silos, cold storage rooms and a model missile.

Dave Wiltshire, now 72, saw himself as a pioneer, one of the few foamers in California who knew how to handle the material.

He liked to tell his son that a good foamer had to be four things: a chemist to get the mixture right, a mechanic to maintain the equipment, an artist to spray it, and a dummy for choosing a career that caked his shoes and speckled his glasses with a hard crust day after day.

Once, while he was foaming the ceiling at a lemon-packing plant, the elder Wiltshire accidentally shot himself in the face, temporarily sealing his eyes shut.

Mike Wiltshire had no desire to make foam his life’s work.

Then in 1977, his father was foaming an old ship the Navy needed for target practice -- 25,000 pounds of foam sprayed below deck would prevent it from sinking.

He fell during the job, breaking several ribs and cracking his skull.

Mike Wiltshire, then 20, dropped out of college to help out with the business. He never left.

It hasn’t been an easy life. The hours are long and the competition brutal.

He describes his company, Wiltshire Urethane Foam Roofing in San Dimas, as “a cockroach that won’t die.”

Lockheed Martin Corp., which is contracted by NASA to build the shuttle’s external fuel tank, gets most of the foam for the job from a large commercial supplier, North Carolina Foam Industries in Mount Airy.

That company’s website includes photographs of commercial roofing, custom packaging, a hot tub and a foam replica of a deer head. One picture shows a space shuttle blasting off.

Steve Riddle, the foam company’s executive vice president, says the foam used on the smooth body of the tank is a tweaked version of roofing foam, with extra protection against extreme temperature changes. It is known as a polyisocyanurate.

Physical properties such as structural stability and adhesion are unchanged, he says.

Each fuel tank, which weighs 1.7 million pounds full, is used once. The foam must stay on until the tank breaks away from the shuttle 69 miles above the Indian Ocean -- about 8 1/2 minutes after liftoff.

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Good foam roofs stay on for decades, which is why every roofer seems to have an opinion on how to resolve the shuttle problem.

Wiltshire, sunburned from too many days atop buildings, subscribes to a popular theory that the foam and the alloy tank expand at different rates as the shuttle heats up, stressing the bond between them.

Michael Payne, a foaming instructor at Intech Equipment & Supply in San Bernardino, says he has seen foam “pop loose” on wine tanks after they are cooled to 40 degrees.

William Lorenz, vice president of marketing at Resin Technology Co. in Ontario, says the space agency has called his company looking for advice on new technology.

He blames the lack of a protective coating.

In the early days of the shuttle, NASA coated the foam with paint. But that step was soon eliminated to save weight -- about 600 pounds. The tank’s distinctive orange color is created by exposure to ultraviolet light.

Roofers always apply a coating to increase strength and screen out ultraviolet light.

“If they put that over the top of the foam, they’d keep the foam,” Lorenz says.

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Jim Anderson, a vice president at Foam Enterprises in Minneapolis, thinks the foam on the shuttle just needs a little extra help during launch.

“Maybe even reinforcing it with chicken wire or some kind of webbing -- maybe something like that would work,” he says.

Among veteran foam sprayers, there is also a sneaking suspicion that inexperience is playing a role in the current shuttle situation.

You can learn a thing or two if you spray a few thousand roofs.

“We’re processing hundreds of thousands of pounds of foam a year,” says Thomas Tisthammer, a roofer in Fort Collins, Colo. “I think I could do it. You bet.”

Lockheed Martin is accustomed to such bravado.

Marion LaNasa, a company spokesman, says he receives e-mail messages every day offering solutions to the foam problem.

It can be a little exasperating.

A man that LaNasa would only identify as a podiatrist recently sent a sample of foam sold in a spray can, proposing it as an alternative material.

“What we’re dealing with is an incredibly complex vehicle in an unimaginable environment that cannot be duplicated on Earth,” LaNasa says.

Having a roof survive a Florida hurricane or decades of Mojave Desert sun is no small feat, either, roofers point out.

Wiltshire notes that the foam on his roofs has been scientifically proven to stick to plywood in winds of 90 mph.

The shuttle reaches about 17,500 mph on liftoff.

“We never tested at that particular speed,” Wiltshire concedes.