Paint Strippers, Types of Strippers
Types of strippers: Strippers fall into three categories: caustic, solvent, and biochemical. There is no shortage of strippers to choose from. Many painters are loyal to one brand. If you’re not yet one of them, consult your dealer, quiz other painters, and experiment.
by Gail Elber
I got when I asked several painters if they used chemical paint strippers:
- “Never! Ever! It gives you brain damage!”
- “Never! Well, except on concrete. Outdoors. And first I get most of the paint off with a heat gun.”
- “Occasionally, but only when I have to.”
After more conversations with painters and paint dealers, I found that many painters don’t understand how strippers work, or how to match a stripper to a job. Although many painters prefer to minimize their use of these chemicals, most painters must use them occasionally. So unless you’re a hard-core “Never! Ever!” painter, take the next few minutes to learn how to use strippers safely and productively.
Strippers fall into three categories: caustic, solvent, and biochemical.
Caustic strippers are water-based solutions with a pH of 13 to 14. Their active ingredient is lye, which may be either potassium hydroxide (known as caustic potash) or sodium hydroxide (caustic soda). In caustic strippers, the lye reacts with the oily component of the paint film, turning it into soap. This reaction with the paint loosens it from the surface. The health risks of caustic strippers include skin burns and lung irritation.
Solvent strippers remove paint by dissolving or softening the bond between the film and substrate, causing the coating to bubble up. The most common solvent is methylene chloride (also called dichloromethane), but alcohol, toluene, acetone, and ketones are often also present.
Methylene chloride-based strippers work very well. However, they pose more potent health risks than caustic strippers do. They temporarily reduce the blood’s capacity to carry oxygen and may cause permanent liver and kidney damage and cancer.
Another solvent is N-methyl-2-pyrrolidone (NMP), often used in combination with dibasic esters (DBE). Although these strippers are promoted as a safer alternative to methylene chloride, their health effects are not yet completely understood. According to the EPA, NMP causes skin swelling, irritation, and blisters. Dibasic esters cling nicely to vertical surfaces, but they work slowly and have been reported to fuzz the surface of wood.
Yet another solvent system is a combination of alcohol, toluene, and methanol. This cocktail works quickly, but it evaporates quickly and is highly flammable. Breathing it can give you brain damage. The fact that it evaporates quickly reduces somewhat the volume of waste you must dispose of.
Biochemical-based stripping agents are another category. The solvents in them are derived from plants. Biochemical-based strippers may include terpenes, from pine or citrus; lactic acids, from corn sugars; dimethylsulfoxide (DMSO), from wood pulp and paper by-products; citric acid; and soy oil. Some of these materials can irritate your skin. In addition to the biochemical ingredients, most of these strippers contain NMP.
Although manufacturers of citrus-based products emphasize their suitability for commercial use, the paint stores in my town don’t report selling a lot of citrus-based strippers to professionals. If customers are concerned about odor, they may be happier if you use a citrus-based stripper. Remind them, though, that citrus-based strippers do contain harmful chemicals, and that the stripper will have to remain on the surface for a long time to work.
Strippers marketed as “safe” or “eco” don’t contain methylene chloride, but they may contain NMP, DBE, biochemical agents, or a combination.
There is no shortage of strippers to choose from. Many painters are loyal to one brand. If you’re not yet one of them, consult your dealer, quiz other painters, and experiment. You may find that you prefer one brand for wood and another for concrete, for example.
Both methylene chloride and caustic strippers will chew through most combinations of alkyd and latex paints. Methylene chloride offers a slight edge in removing epoxies and polyurethanes; caustics perform better than solvents on alkyds. Caustics will darken wood, necessitating a bleaching step if you’re planning to stain it. They’ll also eat aluminum. Caustics have to remain on the surface longer, but many prefer the risks of caustics to the risks of methylene chloride or other solvents. Surface temperature is also a factor in choosing a stripper: caustic strippers don’t work well at temperatures below 50 degrees F. And the logistics of ventilation are important. You don’t want to use methylene chloride if it’s too cold to keep the windows open.
Some strippers are designed for a certain application. Got milk? Caustic strippers designed for coping with milk paint are available (for example, D.O. Siever, www.realmilkpaint.com). Got lead? Strippers meant for lead-based paint contain lime, which bonds with the lead so that it can’t leach out of the waste that you scrape off. Consult your local environmental authorities to see if this will ease your waste disposal problems. Dumond Chemicals and Back to Nature, among others, make strippers of this type. Dumond is also notable for its Peel Away series of products that come with fiber sheets that act as a sort of poultice to hold the stripper on the surface. And Napier Environmental Technologies (www.biowash.com) makes a caustic product specifically formulated for removing stain from decks, fences, and log homes.
Andre Weker of Fiberlock Technologies recommends that you put up test patches of several different removers. Not only will this tell you which type works best on a particular job, but it’ll tell you how long you’ll need to wait before scraping, so you can plan your day.
Read the label. It’ll tell you what precautions to take, whether the container needs to be shaken or stirred, how long the materials should remain on the surface, how to neutralize the surface after stripping, and other important information.
No matter what kind of stripper you use, you’ll want to cover your skin, wear a respirator designed to exclude solvent vapors, and don safety glasses and neoprene or butyl gloves. For all strippers, ventilation is absolutely necessary. Take cabinet doors or other easily removable parts outside to strip. If you must work indoors, to stay within OSHA’s new 25 ppm exposure limit for methylene chloride, the air in the room must change 7-10 times an hour, says Gene Freeman of Bix Manufacturing. To accomplish this, arrange a fan behind you so that the air carries the vapors away from you and out a window, not toward you. Freeman recommends using respirators that supply filtered compressed air from your compressor. Finally, if you’re using a flammable stripper, make sure pilot lights of nearby gas appliances are out.
You can apply strippers with a brush, a roller, a hand spray bottle, or a sprayer, depending on the consistency of the product and the area to be covered. Both solvent-based and caustic based strippers will destroy the rubber, leather, and aluminum parts of a sprayer, but some sprayers can be fitted with neoprene or polyethylene replacements for rubber components and stainless steel replacements for aluminum. If you do a lot of stripping of big areas, consult the manufacturer of your sprayers to determine the cost of dedicating one to stripper.
To brush on a caustic stripper, lay it on thickly in one direction, as if you were icing a cake. Don’t brush over the surface once it’s applied, or you’ll disturb the airtight layer that quickly forms to keep the chemical moist while it does its work. Solvent strippers, whether liquid or gel, don’t need to be applied so thickly.
Leave the area completely while the stripper is working. Your test patches are your guideline for how long to wait. When it’s time, scrape off the goo into a plastic bag or a paint container. A flexible-bladed drywall knife is a good scraper, but dull the edge and round off the corners with a file to minimize the risk of gouging the surface. A plastic scrubbie will get the stuff out of wood pores without leaving rusty fibers as steel wool can. Get into the nooks and crannies with toothpicks, bits of paper, and so forth. If paint remains, give it another application.
When all the paint is gone, wash or neutralize the surface according to the manufacturer’s directions. Caustic strippers can be neutralized with vinegar and water. Some caustic strippers, such as Dumond’s Peel Away, require a proprietary neutralizer. You must test the surface with pH paper to make sure it’s reached pH 7. Solvent strippers can be washed off with mineral spirits. Manufacturers of methylene chloride-based strippers say they clean up with water, but water can fuzz the surface of wood, so it’s best to use mineral spirits if you’re stripping woodwork.
Porous substrates such as wood or concrete will absorb alkaline material from caustic strippers. Even if you neutralize the surface, the absorbed material can bleed to the surface over a period of time. Andre Weker of Fiberlock Technologies recommends neutralizing the surface to pH 7, going away for a few days, then testing the pH again before painting over it.
Whichever kind of stripper you use, thoroughly dry the surface with fans and heat (it may take a week or more, depending on your climate) before further preparation and painting. If you haven’t invested in a moisture meter yet, now would be a good time. A surface that is 15 percent water is too wet to paint; 12 percent is just right. Cedar, cypress, and redwood contain water-soluble material that may bleed through paint if the surface is damp when painted, and these woods may take 60-90 days to dry.
Environmental regulations vary so much from place to place that you had better call your local authorities to determine the best way to dispose of the goo that you scrape off while stripping. Don’t let it get down the drain or into the storm sewer. For a small residential job, you may be able to let the slurry dry outdoors on newspapers, then put them in plastic bags and throw them in the trash. In my town (Eugene, Oregon), the county waste-disposal site has a household hazardous waste day once a month, and some painters go there in an unmarked vehicle to drop off waste from an occasional job. The local paint stores also cooperate on a paint-disposal and recycling program, and they tolerate occasional pails of goo, though large volumes are discouraged. Painters who do more stripping accumulate pails of goo in the shop, and eventually pay a waste-disposal service to get rid of it all at once. Don’t put stripping waste in a metal paint can or mix waste from different jobs in the same container: unpredictable reactions may happen.
Strippers are among the most dangerous chemicals you encounter in your line of work. Although the trend is toward newer solvents that are safer than methylene chloride, you must treat all strippers with respect. Weigh all the considerations, and decide where stripping fits into your business. You may feel comfortable with taking the necessary precautions and using strippers regularly. You may use them as a last resort on troublesome spots after doing all you can with a heat gun. Or - especially if you’re of reproductive age, have health problems, or simply feel that you’re close to absorbing your quota of chemicals for one lifetime — don’t be ashamed if you decide to pass that work to someone else.