TIP: Dry Off NMP ResiduePosted on October 11th, 2010 No comments
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 find this paint stripper very easy to use when I’m not in a hurry. I just brush a thick layer of the stripper onto the surface and walk away for an afternoon, overnight, or longer if necessary, until I can take off all layers of the paint or finish at once.
The problem with this stripper is that some of the solvent remains in the wood for many days, and the solvent can affect the drying of the finish you apply. So, if you want to begin finishing within several days of the stripping, you need to dry out the NMP.
You could do this with heat, of course, but it is usually easier to simply wipe with denatured alcohol or lacquer thinner. Alcohol is less expensive and less toxic. Wipe several times with a damp cloth to dry off the surface. You can feel if you have succeeded; the wood will feel dry. You can also tell you haven’t succeeded if your sandpaper clogs up.