Wash off NMP Residue

Wash off NMP residue with denatured alcohol

Wash off NMP residue with denatured alcohol.

Here’s a caution when stripping paint or finish from furniture or woodwork. Most of the newer “safer” strippers are sold in plastic containers and 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 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 wash or 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, so it’s my solvent of choice. 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.

— Bob Flexner

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3 thoughts on “Wash off NMP Residue

  1. kwhit190211

    I’ve tried the safe stuff which comes in plastic containers. I had to use twice the amount of the stuff &paint was still there. I learned my lesson on that one. No more, you want stripper that works. Buy, the nasty stuff that comes in metal cans. Now that stuff works all the time!

  2. JBrackett

    Except that methylene chloride actually DOES come in plastic containers so you can’t just judge based on the container type.

    1. Bob FlexnerBob Flexner Post author

      The only methylene chloride in plastic containers I’ve seen are heavy-duty 5 gallon and larger containers sold to professional refinishing shops. What brands sell methylene chloride in small containers to consumers?

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