New Paint and Old Houses
As Gozdan pauses near the middle of the paint maze, he points out how
all this theory translates into reality. At a series of mock-ups of
window frames coated with oil paint, he jabs a finger at stringy
hairline cracks on some of the wood and deeper, squarish cracks on
others. Both, he says, are evidence that the oil paint has become too
brittle to keep up with the expansion and contraction of the wood. Then
Gozdan walks to a nearby section where dozens of three-foot pine boards are painted with white latex from a variety of manufacturers. Some boards are gleaming, but after just three years outside, others are
almost bare — a sign, he says, that manufacturers tired to cut corners by
using cheap ingredients.
No, Gozdan won't say which brand is which. That's not the point anyway.
The lessons here are that latex outperforms oil and the expensive
all-acrylic latex works better than less expensive latex with vinyl acrylics. "The most expensive paint," Gozdan says, "is the cheapest in the long run."
Rohm & Haas has a vested interest in this position: Paint gave it a
postwar market for acrylics, which had been going by the ton into
Plexiglas airplane windows. Still, one of the few independent paint
research centers in the country, the U.S. government's Forest Products
Laboratory in Madison, Wisconsin, agrees. The lab compared oil and
latex paints on its own test fences strung across a windy hillside. "We
have twenty-year-old latex that looks as good as if it were new," says
chemist Mark T. Knaebe. The side of a typical house, he says, should
get more protection from two coats of latex over a primer coat than it
would from two coats of modern oil paint over a primer.
No wonder paint salespeople tout the benefits of latex. But what many
don't realize is that all the tests that find latex to be superior have been done by painting over bare wood clapboards or over wood that had only one or two coats of old paint. No one has tested what works best over many layers of old paint. Most houses built before 1950, as well as
many newer ones, are covered with multiple layers of oil paint.
When Gozdan is asked how this might affect the institute's
recommendations, his answer is surprising: "I would never use latex over multiple coats of oil paint. You stand a chance of peeling off all the
paint if you switch." Latex paint can literally pull old oil paint off the house, he says. "I've seen houses where the paint has come off in four-by-eight-foot sheets."
When a flexible layer of latex bonds on top of brittle oil paint the old
paint becomes a thin rope in a tug-of-war. As sunshine hits the wall, the wood and the latex can expand. But the oil paint in the middle is brittle. Now pulled with double force, it either cracks or loosens its grip on the wood underneath. "The latex tends to accelerate the paint loss," says Carl Minchew, director of technical services for Benjamin Moore & Co.
Gary Barrett, director of technical services for the Painting &
Decorating Contractors of America, says the stress on the old oil paint
is greatest during the few weeks it takes latex to cure, although the
results may take months or years to become fully evident. "It's the shrink factor of latex," Barrett says. "It has to coalesce, or it can't cure."
The force of this effect varies. Often houses with layers of old oil paint can be successfully covered with modern latex. But when it doesn't work, the results may be disastrous. "It's very unpredictable," says John G. Stauffer, director of the Paint Quality Institute. To be safe, Gozdan and Stauffer say, people who have houses with more than five layers of oil paint are best to stick with oil.
Many others in the industry are not so cautious. Homeowners can safely
recoat even many layers of oil paint with latex as long as the old paint
is adhering well and is in good shape, says David Maurer, manager of product development and color delivery for the Gildden Co., which sold the first latex paint in 1948. "If, categorically, latex going over oil
was a problem, I don't think we'd have any latex paint, or we'd have
latex limited to new construction, and that's certainly not the case, " he says. "But I will say that if you have a lost of loosely adhering — and it is common on older houses to see oil paints fractured right down to the surface — latex paints can hasten the demise by putting pressure on the poor oil paint. I think oil paint makes a better Band-Aid,"
Not long ago, a friend of Maurer's sought advice on how to repaint an
old house with wood shakes. "It was the old oil syndrome," Maurer says.
The paint was thick and cracking, and the options were not good: Spend a lot of money stripping off all the paint, or spend less money for a
repainting that wouldn't last. "I told him the good answer was to
remove it all, but the short-term answer was to put another layer of oil
on top. At least he wouldn't be creating a new problem. He'd just be
stalling the inevitable."
To stall the inevitable as long as possible, homeowners can do periodic touch-ups with oil paint instead of recoats. The National Park Service, custodian of many old houses, has found that homeowners have more time to play with than they might think. Oil paint is most likely to crack, the service says, when it is more than a sixteenth of an inch thick, the equivalent of 16 to 30 coats.
Homeowners who stick with oil may find the paint thicker and not as
durable as it once was. Many manufacturers have changed their alkyd formulas to meet clean-air rules in effect in six states. But even if
similar rules take effect nationwide next year, as expected, it still
will be possible — and legal — to buy oil paint the way it used to be made.
Oddly enough, manufacturers can continue to sell high-solvent paint
simply by relabeling it "quick-dry enamel," "industrial maintenance
coating" or "marine paint." Manufacturers can also sell high-solvent oil paint by the quart, although buying it this way instead of by the gallon typically doubles the cost. And top-quality but expensive oil paint that meets most of the clean-air rules is available from several European manufacturers who, unlike their US counterparts, have continued to invest research money in oil formulas. One company, Fine Paints of Europe, sells a "problem house" oil paint formulated to allow water vapor to pass through.
Eventually, every house painted with oil will peel, says Minchew of
Benjamin Moore, "because that's what oil paints do. They continue to
oxidize and get brittle." Once a house reaches this point, he says,
owners have two choices, First they can scrape off all the peeling
paint, prime the bare spots and repaint with latex. Areas that weren't
scraped bare will then peel, and the owners can repeat the process until
eventually they have a house entirely covered in latex paint that
sticks. Second, they can choose a faster, less ugly method: Strip the
house down to bare wood and start over, either with latex paint or a
semi-transparent oil stain. (These stains don't form a film, so there's
nothing to peel.)
Unfortunately, the best solution — stripping and staring over — is also the most expensive, In fact, it can be so expensive that new siding may seem like a better option. The expense may even make the most faithful old-house lover consider the unthinkable: vinyl siding. When Dee worked out the numbers for his house, he discovered it would cost only slightly more to rip off all the old shingles, nail up new ones and repaint. Vinyl siding was even cheaper. "Maybe that's the best solution," he says.
