On average, Americans change addresses every seven years.

Ask demographers for a reason, and they talk about how we are a restless people, never content with what we have, perpetually looking for something new or different.

But the real reason may be that no homeowner wants to paint the same house twice.

Statistics show that painting is the one do-it-yourself job most people take on. But painting isn't as easy as it looks.

Just ask the people in charge of the Rohm and Haas Paint Quality Institute. They monitor and evaluate how well the ingredients that go into paint perform over the long haul to determine what works best and what lasts longest.

On a 6.5-acre site 20 miles northwest of Philadelphia that employees call "the farm," 25,000 separate paint formulations are exposed to the weather on fences that, from the northbound lanes of adjacent Route 309, appear at first to be solar panels.

The staff tests for durability and color retention, and for which paints develop mildew more quickly than others. The staff also tries to determine which paint adheres best to which surface.

The testers have discovered some interesting things in the nearly 46 years that the Rohm and Haas Co., which supplies acrylic binders--substances that hold paint together--has been testing it.

For example, said Debbie Zimmer, the institute's marketing communications manager, aluminum and vinyl siding can be painted.

"Most people bought aluminum siding because it was maintenance-free and didn't need to be painted, but over the years the factory-applied surface coating wears and weathers just like ordinary paint," she said.

"You can change the color of the siding to spruce it up to get the house ready for sale," Zimmer said.

The surface should be power-washed first to remove years of built-up grime. A fine powder remains on the surface. This is called "chalking" and is normal, but completely removing it will help the new paint adhere to the surface.

"The emphasis is on using a top-quality paint," said Terry Gillis, a sales support manager at the Paint Quality Institute. "And that means an exterior acrylic latex paint, which has been shown to work best because of its superior adhesion, durability and fade-resistance characteristics."

Acrylic latex paints have additives that resist mildew and provide a thick, uniform coat, she said.

Vinyl siding, too, can be painted, but the color of the paint should be no darker than the original color of the siding, Zimmer said.

"That's because darker colors cause the vinyl to buckle when the paint reacts with sunlight," Gillis said, pointing to a sample panel on one of the fences in the testing field. The vinyl siding in question looked like rubber but felt like paper.

Consumers and professionals spend billions of dollars a year on paint, and one of the jobs of the Paint Quality Institute is to make sure that the money is being spent wisely.

"The main argument we present is that better quality means better performance," Zimmer said. "To do so, we hold regular training sessions here for sales representatives of the major paint manufacturers. We emphasize that understanding the components in a can of paint can help the end users--the do-it-yourselfers and the professionals--[do] a better paint job.

"They need to know what they are selling," Zimmer said.

Although the institute tests paints for individual manufacturers, the results are "generic, and not which brand is better than the other," Zimmer said. "The raw materials, the polymers, that form the basis of the paints and coatings are constantly being tested, and new ingredients are being developed all the time."

The paints and stains are being tested not only on wood, aluminum and vinyl, but also on masonry and on new building materials such as wood composites, she said, in an effort to develop coatings for the future.

Tests are conducted worldwide and in other parts of the United States--Illinois, Florida, Los Angeles and North Carolina, she said.

Manufacturers use the test information, which has been computerized since 1970, to formulate paint to perform well under varying conditions.

The tests are designed to accelerate the effects of climate. For example, some of the panels face south, offering the greatest exposure to the sun. Some panels face north to gauge the speed at which mildew occurs.

Some wood panels are kept bare for three months to simulate chalking, and then painted to see how well or badly the paint adheres. Nails are hammered into some boards, and then the whole piece is primed and painted to see whether the nail heads will rust and bleed into the surface coat.

"We only do a few of those because one of those panels costs $300 to make," Gillis said.

When testing pigmentation, blue paint is used because it shows fading better and more quickly, she said.

The testers are highly trained technicians who can detect the slightest change in every one of the painted surfaces, Zimmer said.

"To guarantee accuracy in their observations, the testers are retested constantly," she said.

Every available surface at the "farm" is used for testing, including the stucco exterior of the farmhouse that serves as the office. It is being used to test performance of some of the "future-surface" paints that Zimmer mentioned--in this case, masonry.

Conventional wisdom has dictated the use of exterior latex paint for masonry. But Rohm & Haas has been developing binders and additives for specialty coatings, including elastomeric wall coatings made with 100 percent acrylic.

One side of the farmhouse has been painted with elastomeric paint, which goes on much thicker than traditional stucco paint. The paint, Gillis pointed out, not only covered the cracks in the stucco, but sealed out moisture from wind-driven rain.

The paint's elasticity stretches and bridges cracks on outside walls. The paint also resists dirt, Gillis said, pointing to dirt streaks on the side of the house painted with latex stucco paint.

Efforts are being made to develop paints with low levels of volatile organic compounds, known as VOCs. Combined with other airborne contaminants and ultraviolet light, some VOCs create lower-atmospheric ozone, which contributes to smog.

While laws require the industry to reduce the VOCs in paint, testing has found that reducing these levels has not affected the overall performance of latex paints, but that it has limited the performance of solvent-based paints that have much higher levels of VOCs.

The reformulated latex paints not only have lower levels of VOCs, they have less odor. They are being used in hospitals, nursing homes, schools and hotels.

"That's the beauty of acrylic latex paints," Zimmer said. "The technology is enabling manufacturers to reduce the levels of VOCs while maintaining quality."

But while a top-quality paint is key to a professional, long-lasting paint job, it isn't the only ingredient, Zimmer said.

"No matter how good the paint is, it won't perform properly without proper surface preparation," she said. "And when you use top-of-the-line paint, you're doomed to failure if you skimp on tools, so make sure you buy the right brushes and rollers for the job."

Information from the Paint Quality Institute is available at www.paintquality.com