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Used with care, chemical strippers peel off old, unwanted paint.

Scrape Off
Photo by David Carmack
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As the general contractor for This Old House, Tom Silva seems to be in a constant fight to liberate houses from the grip of old paint. Among his more recent battlegrounds were the TV show's 1997 project house in Milton, Massachusetts, where 18 rough, peeling layers, many containing lead, obscured details of an interior staircase and encased the original clapboards; the 1998 project house in Watertown, Mass., with its paint-clogged mantels and doors; and the 2000 project house in Charlestown, Mass., where some of the exterior brick had been buried beneath a mishmash of latex, milk, and lead paints. In each case, Tom turned to chemical strippers, formulations that dissolve the chemical bonds in a coating so that it can be scraped away. "They're like magic," he says. "You brush or spray a stripper on and scrape soft paint off, sometimes several layers in one stroke."

Chemical stripping is one of the four ways Tom can get rid of old paint. One is to rip out the old material, paint and all, and replace it with new, but sometimes that doesn't make sense. "A piece of wood that's solid walnut or gum would be very expensive to replace, especially if it has a special profile," Tom says. And some details, like the intricate, carved gable detail in Watertown, are irreplaceable. Power sanding is the fastest removal method, but also the one most likely to damage the underlying surface and blow dust into the air, a serious hazard if the paint contains lead. Softening paint with heat guns is a gentler approach, but the process is tedious, often chars the wood, and can create toxic aerosols if the paint contains lead. Stripping with chemicals is also slow and messy, but done correctly it's the surest way to eliminate paint and preserve the wood. "I'm a firm believer in stripping, under the right circumstances," Tom says.

The first and perhaps biggest challenge is figuring out which chemical stripper to use. Buyers have to consider a number of factors, including the amount and kind of material being stripped, the type of surface the stripper is applied to, how quickly and effectively it works, and what gear is needed to use it safely. The starting point for making an informed decision is to look at the ingredients. All strippers contain one of five basic paint-softening substances: solvents such as methylene chloride, N-methyl pyrrolidone (NMP), dibasic ester (DBE), and acetone, toluene, and methanol (ATM); and highly alkaline caustics such as lye. Each one has its strengths and weaknesses, and each one—even if promoted as "safe"—needs to be treated with caution. "They're all potentially hazardous," says Ken Giles, a spokesman at the U.S. Consumer Product Safety Commission (CSPC). But, he adds, the Commission has concluded that all strippers being sold to consumers can be used safely. "If they could not, we would have to ban them."

As the general contractor for This Old House, Tom Silva seems to be in a constant fight to liberate houses from the grip of old paint. Among his more recent battlegrounds were the TV show's 1997 project house in Milton, Massachusetts, where 18 rough, peeling layers, many containing lead, obscured details of an interior staircase and encased the original clapboards; the 1998 project house in Watertown, Mass., with its paint-clogged mantels and doors; and the 2000 project house in Charlestown, Mass., where some of the exterior brick had been buried beneath a mishmash of latex, milk, and lead paints. In each case, Tom turned to chemical strippers, formulations that dissolve the chemical bonds in a coating so that it can be scraped away. "They're like magic," he says. "You brush or spray a stripper on and scrape soft paint off, sometimes several layers in one stroke."

Chemical stripping is one of the four ways Tom can get rid of old paint. One is to rip out the old material, paint and all, and replace it with new, but sometimes that doesn't make sense. "A piece of wood that's solid walnut or gum would be very expensive to replace, especially if it has a special profile," Tom says. And some details, like the intricate, carved gable detail in Watertown, are irreplaceable. Power sanding is the fastest removal method, but also the one most likely to damage the underlying surface and blow dust into the air, a serious hazard if the paint contains lead. Softening paint with heat guns is a gentler approach, but the process is tedious, often chars the wood, and can create toxic aerosols if the paint contains lead. Stripping with chemicals is also slow and messy, but done correctly it's the surest way to eliminate paint and preserve the wood. "I'm a firm believer in stripping, under the right circumstances," Tom says.

The first and perhaps biggest challenge is figuring out which chemical stripper to use. Buyers have to consider a number of factors, including the amount and kind of material being stripped, the type of surface the stripper is applied to, how quickly and effectively it works, and what gear is needed to use it safely. The starting point for making an informed decision is to look at the ingredients. All strippers contain one of five basic paint-softening substances: solvents such as methylene chloride, N-methyl pyrrolidone (NMP), dibasic ester (DBE), and acetone, toluene, and methanol (ATM); and highly alkaline caustics such as lye. Each one has its strengths and weaknesses, and each one—even if promoted as "safe"—needs to be treated with caution. "They're all potentially hazardous," says Ken Giles, a spokesman at the U.S. Consumer Product Safety Commission (CSPC). But, he adds, the Commission has concluded that all strippers being sold to consumers can be used safely. "If they could not, we would have to ban them."

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Tom Silva stripping paint
To remove paint from an old window casing, John Dee brushes on a thick coat of a low-fume stripper (1) waits 12 to 24 hours for the paint to soften.
Strippers based on the solvent methylene chloride—also known as dichloromethane—have dominated the market for the past half century. They are speedy, nonflammable, effective on virtually all coatings except milk paint, and do not damage wood, metal, or masonry. Methylene chloride molecules are so small that they easily slip between the molecules in a coating's hard outer film, rapidly softening the film and releasing its grip. According to Thomas Wollbrinck, a paintings conservator who wrote about the composition of chemical strippers for the Journal of the American Institute for Conservation, the solvent works by swelling the paint to 10 times its original volume. The bubbles and blisters created from this swelling ultimately release the paint from the substrate.

The problem with these hyperkinetic molecules is that they also rapidly evaporate, which slows down the blistering process. To keep the solvent working on a finish as long as possible, manufacturers typically add paraffin, which forms a skin when exposed to air. That's why these strippers should be brushed on thickly—stroking only in one direction—over one small section at a time and then left undisturbed for about 15 or 20 minutes. At that point, if the paint is not removed or more stripper added, the finish will reharden and the paraffin will then inhibit additional stripper from working. After the old paint is scraped off but before new paint is applied, a wipe-down with denatured alcohol is the best way to remove any waxy residue. (Some manufacturers add surfactants—soaps—so that stripper residue can be washed off with water or mineral spirits.)

Methylene chloride's speedy evaporation rate also increases the risk of inhalation. Once breathed in, it metabolizes into carbon monoxide, which reduces the blood's ability to carry oxygen and makes the heart work harder. According to the EPA, short-term exposure can cause dizziness and lack of coordination; high exposures over an extended period can damage the liver and kidneys and may cause cancer. In an enclosed, poorly ventilated space, the vapor can overwhelm even the best organic–vapor respirators in as little as 15 minutes. Providing excellent ventilation is key to safety—then a respirator can do its job—but the only sure protection from vapors is to wear a respirator with an air supply. Methylene chloride that comes in contact with skin creates an immediate burning sensation (which can be neutralized with water), so wear long sleeves, trousers, and chemical-resistant plastic–laminated gloves. (Neoprene or butyl gloves can become ineffective in as little as six minutes.) Protective goggles are a must as well. Methylene chloride that gets in the eyes can cause severe burns and should be flushed out with plenty of water for several minutes. After that, the labels recommend, visit a doctor.
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stripping paint
(2) Then gently scrapes it off .
With all the practical, health, and safety concerns surrounding methylene chloride, it's not surprising that some manufacturers have come up with alternatives. The most common now on the market is N-methyl pyrrolidone, often called NMP. Unlike methylene chloride, NMP evaporates very slowly, so it remains active on paint long enough to soften and release many layers at once. The key with NMP is patience; it needs more time to work than methylene chloride.

"There's no quick bubbling," says Janice Nachbar, national sales manager for the Back to Nature line of NMP strippers. "It's not burning up the paint, just dissolving the binders—the oils and latexes that keep a paint film intact." Painting and decorating contactor John Dee, who has used NMP strippers on several projects, has found that he can spread them over a larger area with little risk that the solvent will evaporate before he has time to remove all the softened paint. And because there's no waxy residue, he can go right from scraping to painting with no intermediate wash. "It's very wood-friendly," he says.

But as far as being people-friendly, NMP has a mixed scorecard. Claims that it's safer than methylene chloride are based on its low evaporation rate, which does minimize the risk of inhalation unless the stripper is sprayed. Still, NMP should be used in a well-ventilated space. Also, the liquid is a skin irritant, and it can cause a burning sensation for up to two days after initial contact unless quickly washed off with water. Dressing in sleeves and trousers reduces the chance of NMP getting on skin, but the only suitable protection for hands is butyl-rubber, nitrile, or neoprene gloves. "Latex gloves like you get at a supermarket are not enough," Gilles says.

The group of solvent-based strippers known as dibasic esters, or DBEs, is another of the "safe" finish removers now on store shelves. Like NMPs, with which they are often paired, DBEs evaporate slowly and can work through many paint layers at once, although it takes even longer than NMP. When using DBE strippers, contractors will often paint on a thick layer and cover it overnight with plastic wrap. When it comes time to remove it, the gummy residue clings to the wrap, making scraping less messy.

DBEs have long been used in hand cleaners, and have been marketed as the "safest" of all strippers. But the CPSC became concerned about those marketing claims after some people reported blurred vision when working with the solvent in poorly ventilated spaces.

Industry-sponsored testing in conjunction with the Environmental Protection Agency is underway to confirm or refute those reports; final data are not yet available.
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paint stripping with a casing
(3) "Let the stripper do the work," Dee says. "Then, tool it off without damaging the wood beneath." This casing required two applications: one for the latex paint, then one for the oil.
The fourth solvent-type stripper is a combination of acetone, toluene, and methanol (ATM). Like methylene chloride, these highly volatile chemicals can be extremely effective in removing paint, especially when formulated with waxes and thickeners that trap the active ingredients close to the surface. Phillip Pennington, whose Star 10 strippers fall in this category, says these are the same solvents found in cans of high-performance paint, where they keep the solid ingredients in solution. "Our stripper puts the solvent back into the paint, but without turning the coatings to liquid," he says. "It breaks the adhesion or bonds where the paint stuck to the wood." An ATM stripper removed the paint from an old mantel at the This Old House project in Watertown and impressed Tom with its effectiveness. "The stuff was amazing," he says. "We sprayed it on, left it overnight, and by morning it had taken the finish right off."

Yet according to the manufacturer's material safety data sheets, if inhaled or absorbed through skin contact, ATM strippers can irritate the eyes and skin, damage the lungs, liver, kidney, and heart, as well as the central nervous and reproductive systems, and can be fatal if swallowed. They need to be used with plenty of ventilation and the proper safety gear, including splash-proof goggles, butyl or plastic-laminate gloves, and a respirator fitted with organic-vapor cartridges. These strippers are also highly flammable—cigarettes, pilot lights, and sparks from electrical equipment can set off an explosion if the vapors concentrate sufficiently.

The only fumeless way for consumers to remove paint is with caustic, or alkaline, strippers. Made with caustic soda, lye, or potash, they eat through many layers of coatings the same way lye-based drain cleaners dissolve the gunk in a clogged pipe. This slow but steady chemical action is remarkably effective, but once the paint is gone, alkaline strippers don't stop. They'll darken and desiccate exposed wood and will attack the new finish unless neutralized with an acid rinse. Skin and eyes are equally at risk, making goggles, chemical-resistant gloves, and protective clothing essential for anyone applying or removing the stripper.

Because it's hard to know how deeply and uniformly the neutralizer has done its work, repainting is a gamble. "I usually stay away from alkaline strippers on wood," says Dee, "except on decks or places where I can rinse the area with plenty of water and an acid." Everywhere else, he uses methylene chloride when he's in a hurry and a thick NMP stripper when he has more time. Then he steps back and moves on to the phase every painter loves: applying a fresh finish.
 
 

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