Metal finishing Q&As since 1989

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Getting that last bit of paint off

I'm involved in a project where we're reconditioning architectural metal products. These parts are mild steel that have been painted many, many times over the years.

We use a fairly standard methylene chloride/surfactant/organic base formulation stripper. It takes off ALMOST everything...but there are little nooks and crannies that are very hard to get at with mechanical abrasive treatments that we use. It would be great to have some kind of chemical that would remove that last bit of paint, because what we're doing now is very time consuming and labor intensive.

I've thought of some kind of aqueous cleaner, perhaps a heated caustic/surfactant brew, or a mildly acidic cleaner, might just dissolve whatever is holding those last stubborn flecks on. Cost is a concern, as well. My client has many years of experience in the field, and is a little skeptical that there's any better fix than good old fashioned elbow grease...can anyone offer any help?

Dave Wichern
Consultant - The Bronx, New York
2007

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Hi Dave. It is a bit different to see a frequent contributor with a question.

One approach would be high pressure water and that would be a lot faster if you had the capability to pump a thin suspension of relatively fine aluminum oxide. We had a cabinet made in England and would add the worn out fines from the pressure blast cabinet to the sump.We could control it to the point of taking off a chromate coating with no measurable loss of plated material to taking off electroplating with little loss of parent material.

The next option that I see would be a small blast gun about the size of an air brush. I know that there are many sizes of these and some are used for engraving and others for glass etch and finally, large ones for engraving tombstones.
A small to medium size with appropriate grit would be a lot faster than elbow grease and would leave a finish compatible with your blast operation.
Jim

James Watts
- Navarre, Florida
2007

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Blasting is quicker and cheaper than chemical paint strippers. You can use sand. If sand is too coarse, you can use walnut shell media [on eBay or Amazon] or plastic. Still gentler (and leaving no residue) is frozen carbon dioxide.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
2007

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January 12, 2008

What solved the problem:

Direct application of 50% caustic soda [affil links] . It dissolved the paint right off.

Dave Wichern
Consultant - The Bronx, New York