Popular Woodworking 2000-06 № 115, страница 59
Flexner on Finishing Paint and Varnish Removers Learn the differences between the six types of strippers on the market. No step in refinishing is as messy and unpleasant as stripping off old paint or finish. Though stripping can't be made clean and enjoyable, it does help to know something about the stripping products available so you can choose intelligently among them. Fortunately, in the case of strippers (unlike other finishing products), the primary ingredients are almost always listed on the container, so it's possible to make sense of the products by separating them into types. There are four types of strippers that are solvents and one type that is lye. You also can buy a stripper that combines two of the solvents, so there are actually six types of strippers on the market today: • Methylene chloride (MC) • Acetone, toluene and methanol (ATM) • N-methyl pyrrolidone (NMP) • Di-basic esters (DBE) • A combination of methylene chloride plus acetone, toluene and methanol (MC/ATM) • Lye MC, ATM and MC/ATM are available in various thicknesses, ranging from liquid to semi-paste. The thickness makes a difference in how well the stripper clings to vertical surfaces, but not in its strength or effectiveness. Lye is available in both a powder form, which you have to mix with water, and in paste form, which is ready for use. Methylene Chloride (MC) The strongest and fastest-acting of the five solvent types is methylene chloride. You can identify this stripper in two easy ways: by the statement it's "non-flammable" on the can, and by the listing of only MC and methanol as the solvents. (A little methanol is always added to MC as an activator.) Methylene chloride is very effective at removing all types of coatings, and even though it is moderately expensive, it has been the primary solvent used in strippers for the last four decades. About 15 years ago, the Environmental Protection Agency listed MC as a probable human carcinogen, though the evidence for such a listing remains highly controversial. Some manufacturers add acids or alkalies to their MC strippers to increase their strength, but these additives are seldom listed on the container. Almost all manufacturers add wax, which rises to the surface and retards the evaporation of the MC. The wax residue must be washed off before finishing the wood, or the finish may not bond well. Manufacturers misleading-ly call this washing step "neutralizing." Acetone,Toluene, Methanol (ATM) This is the cheapest solvent stripper and is essentially nothing more than lacquer thinner. It's effective at removing shellac and lacquer, but is slow on all other coatings. When manufacturers add wax to slow evaporation, they call the remover a "stripper." When they don't add wax, they call it a "refinisher." To use refinisher, you must work on very small sections at a time due to the fast evaporation of the solvents. Other members of the three solvent families — ketones, petroleum distillates and alcohols — are sometimes added to or substituted for acetone, toluene and methanol to change evaporation rates, but the stripper is still in the ATM category. All of the solvents used in this category are extremely flammable, and mention of this is made on the can. MC/ATM By combining MC and ATM in varying proportions, manufacturers produce a stripper that is in between in both effectiveness and cost. Combination strippers list a number of solvents, including methylene chloride, and also warn of flammabil-ity. These strippers are effective on all but the most stubborn coatings. N-Methyl Pyrrolidone (NMP) The possibility that MC could cause cancer and the high flammability of ATM and 10 Popular Woodworking June 2000 |
