PROS AND CONS OF TYPES OF PAINT REMOVAL CHEMICALS USED FOR PAINTSTRIPPING
First appeared in PROFESSIONAL REFINISHING MAGAZINE, NOVEMBER/DECEMBER 1998
BY DEAN CAMENARES
Stripping on-site is a different animal than doing it in the controlled confines of a shop. It's much more laborious, mainly because you can't use dip tanks or flow-stripping techniques. Also, because you're sometimes dealing with different types of paint with their distinctive characteristics, circumstances often require unusual flexibility and frequently require you to use more than one type of stripping product.
These removers consist mainly of lye (sodium hydroxide) and are considered non-toxic and environmentally friendly although you don't want to get any in your eyes or on your skin unless you like wickedly strong burning sensations. These products work slowly (usually taking 12 to 24 hours); that's generally not much of a problem, so long as you can secure the stripping area to a reasonable degree. They are effective over a range of older coatings (including milk and calcimine paints) and work fairly well on some newer paints, too. They will not, however, strip varnish or lacquer. The biggest drawback to caustic strippers is the fact that their alkaline nature changes the pH of the wood, which means you have to go to the extra step of neutralizing the wood with acid. Also, even after multiple washings, the wood Is susceptible to "bleeding:' which can cause finish failure even months after application. Finally, caustics can cause severe grain raising. All in all, because of these limitations, we don't use too much caustic stripper although we do keep it on hand as a last resort with really stubborn old paint.
These solvents are the main ingredients in a variety of flammable stripping products and are very effective in stripping shellac, lacquer and some varnishes. (They also work fairly well on newer paints but are ineffective with older paints.) These products require an after-wash solvent, such as lacquer thinner, to clean any residue from the wood. This is actually a good thing, because repeated applications will help "float out" paint from crevices and wood pores, which can be a tremendous help in some situations. On the downside, flammability is a huge concern. The base solvents evaporate very quickly, so waxes are added to these strippers to slow down the drying time and allow the chemicals to work. Unfortunately, this combination of wax and flammable solvent is a potential hazard: All it takes is one spark from a scraper pulling over an old nail head and you're up in smoke. Additionally, these solvents do have health risks associated with their use. Generally speaking, we use these strippers only when absolutely necessary and then only on a limited and carefully controlled basis.
The workhorse of the stripping industry, this stuff is very effective on clear finishes and on most paints as well. It works quickly by delaminating paint layers rather than liquefying them. Still, there are much-publicized problems with MC strippers and layers of regulation on the horizon. With reasonable precautions, however, MC is effective as a primary stripping agent especially in its gel form, and can be particularly helpful in its liquid form as a final cleansing wash.
These chemicals with the excruciatingly long names are the main ingredients in a fairly new class of strippers developed to overcome both the real and perceived disadvantages of the other removers on the market. With no known health-related or environmental problems, these solvents work very slowly. In fact, they can take up to a week or more to do the job, although you'll usually see results in 24 to 12 hours, depending on the coating you're removing. Strippers based on these solvents are very good at getting the bulk of old paint and finish off, allowing you to do a final clean up with much less overall labor. The biggest drawback is cost, which at this writing in the New York area is about $45 per gallon, roughly three to five times the cost of other removers. Still, their effectiveness has motivated us to figure out ways to get around their slow natures with creative scheduling. Often, we'll coat the surface with this stuff on Monday and then return on Thursday to scrape it off.
I make no bones about the fact that I prefer to use an n-methyl pyrollidone (NMP) type product for stripping architectural woodwork. Let's assume that you, for whatever reason, have decided to use a different remover for your project.
That's not an uncommon decision, because many refinishers are put off by the fact that NMP-type products cost about four times as much as products that use methylene chloride to get the job done. There also certain kinds of paint with which NMP products just don't get job done - although that's rare, in my experience. Or maybe your project is a small one and you won't be spending many days on the job. perhaps you're stripping shellac or thin coats of varnish and you want something that gets you in and out fast.
If NMP is just not the right product for one of my projects, I usually turn to a standard, semi-paste remover from the methylene-chloride family. MC-based removers are highly effective - and relatively inexpensive.
One of their drawbacks is that MC itself is a suspected carcinogen and more and more limitations are being placed on its use. I don't want to get into the controversy and the complexities; suffice it to say that these products offer a workable alternative when NMP isn't the remover of choice.
Applying a semi-paste MC product involves a method similar to one I use with NMP-type products, but you'll definitely want to us brush (it's way too thin for effective troweling). Also, it'll dry far more quickly as it is absorbed by the finish and evaporates into the air. By dipping your chip brush into a plastic quart container and spre ing the remover over the wood surface in even, one-way strokes (don't brush back and forth!), you can get effective coverage and stripping action over small areas at one time.
(Dean Camenares is a pioneer and technical authority on interior architectural wood stripping, refinishing and general restoration. He is the principal of East End Woodstrippers.)