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."
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, a company history said.
His bosses were unimpressed. "At best, a material for making imitation Emmentaler cheese," they noted in a 1941 lab 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.
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 in San Bernardino, Calif., 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, Calif., 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.
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-mails 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.
Alan Zarembo is a reporter for the Los Angeles Times.