This Old House painter John Dee calls his neighbors Robert and Andrea Bowler "the epitome of diligent homeowners." They bought their postwar Colonial in May two years ago, and a month later Andrea was down at the local hardware store, picking out new beige paint to lighten up the gloomy exterior. Soon Robert was up on the ladder, hard at work. "It wasn't easy," he says. "I scraped the whole house, rented a water gun, primed everything. I put two coats of paint over that. I did it when I got home from work, I did it on Saturdays. It took me the whole summer. It looked so good." But within a year, as the Bowlers watched in horror, their labor-intensive paint job — and everything underneath — was flaking off in leathery sheets. The paint detached with such determination that some chips were embedded with cedar splinters from the underlying siding. Layers of paint that had bonded to the house for decades came loose. "You can generally tell if you have a house that is going to peel if you probe around a bit," Dee says. "But my neighbors had no previous paint problems, and they went by the book." Dee has understandable sympathy for the Bowlers: Not long after his house was repainted, it began peeling so badly the south wall looked like a head of hair after a botched perm. "It's a total blowout," he says. About one in 10 paint job goes awry, says David Chupka, a technical manager for the Sherwin Williams Co. Often it's because of cutting corners — not sanding, not scrubbing, painting just before a storm,ignoring long-term moisture penetration. But people who own old homes can do everything they're told by paint salesmen and follow labels devotedly and still wind up with paint that peels. If they've hired someone to do the work, at prices that can rival the cost of a new car, peeling paint can begin to look like paper dollars floating off with each breeze.
William C. Feist thinks he knows why. The problem can occur when an old house with multiple layers of oil-base paint is coated with a modern water-base paint, says Feist who headed the federal government's house paint research program for 20 years. "The homeowners decide to upgrade and put on a good latex paint. But that last coat of a new type of paint can be sufficient to cause catastrophic failure, often right down to bare wood. " When people in the paint industry have a problem they often consult with the chemical company that supplies them with the ingredients they put in their cans. In the United States, almost all paint companies turn to Rohm & Haas and its Paint Quality Institute in Spring House, Pennsylvania, near Philadelphia. There, in a six-acre field draped with two miles of odd-looking fences, 25,000 paint samples are in a contest with time, weather and the sun. On a blustery day last winter, the institute's technical director, Walter J. Gozdan, led the way through this maze, happy to talk about the intricacies of what people in the paint industry like to call coatings.
Essentially, he says, there are two kinds of house paint: oil (also called alkyd because of the alcohols and acids used to make a synthetic oil) and so-called latex (which, it turns out, has no rubber in it). Both consist of three main components: a pigment, a binder that glues the pigment to a surface as the paint dries and a solvent that makes the mixture loose enough to brush on. Oil paint forms a tough plastic film as the binder reacts with oxygen in the air. The binder can be a natural oil, such as linseed squeezed out of flaxseed, or oil modified with alkyds. Latex paint forms a flexible film as water evaporates and the once-floating spheres of binder and pigment move closer together and fuse. Latex paint was inverted at the end of World War II using synthetic rubber as the binder. Today the binder is most often a pure acrylic, a vinyl-acrylic or a vinyl acetate. The critical difference between oil and latex paints is that they do not cure in the same way. Oil paint never stops curing. As it ages, it continues to oxidize, becoming more and more brittle. Latex cures in about two weeks and stays pliable. Oil paint generally adheres better to problem surfaces because the oils are small enough to seep into the wood or microscopic openings in old, even chalky paint. The resins in latex paint are generally too big to seep into anything. But that can be advantageous. The gaps between the larger particles in latex paint allow water vapor to pass through. This makes latex less likely to peel from homes with excessive interior moisture.