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Expert's Corner — strippers

So-Called “Green” Paint Strippers

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There are an increasing number of so-called “green” paint strippers on the market with problems you need to be aware of. These strippers are easy to identify by their packaging, which is always in plastic containers. Traditional methylene-chloride and flammable-solvent strippers are always in metal cans. The packaging tells you everything you need to know about the strength of the stripper. Strong solvents dissolve plastic. So the green strippers use weaker solvents. These strippers are still very effective, however. If given enough time, they will liquefy or loosen the bond of almost all paints and finishes. There are four things...

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TIP: Wash Off Stripper Wax

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Directions on cans of paint-and-varnish remover instruct to “neutralize” the stripper as a final step. This is misleading and often leads to finishing problems. The instruction is misleading because there is nothing in paint strippers that needs to be neutralized. “Neutralizing” refers to acids and bases, not solvents. What needs to be done with all paint strippers sold in metal cans is remove the wax they contain. Manufacturers add wax to these products to retard evaporation so the stripper remains in contact with the paint or finish longer. This wax will retard the drying and weaken the bonding of most...

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TIP: Dry Off NMP Residue

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Paint and varnish removers sold in plastic containers contain the solvent n-methyl pyrrolidone (NMP) as the active ingredient. This solvent is relatively expensive, so manufacturers often mix in other solvents to reduce the cost. But it’s the NMP that does the majority of the work. NMP has less solvent strength than the methylene chloride and the other solvents used in strippers sold in cans. Just the packaging, plastic vs. metal, tells you this. The reason NMP is still effective is that it evaporates extremely slowly, so it can remain wet on the paint or finish for days if necessary. I...

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TIP: Oil and Spontaneous Combustion

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Drying oils, especially linseed oil, are the only finishing materials that spontaneously combust. Solvents don’t spontaneously combust, paint strippers (including paint or finish residue) don’t spontaneously combust, and no type of varnish spontaneously combusts. It’s not totally clear whether 100% tung oil can spontaneously combust, so treat it like it does. As linseed oil dries, it generates heat as a byproduct. If you wad up linseed-oil rags or pile them on top of each other, the heat generated in the middle can’t dissipate. It builds up until it reaches the flash point of the cloth and it bursts into flame....

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