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Thread: Teaching myself by tearing apart a piece of junk

  1. #1
    Registered User belbein's Avatar
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    Default Teaching myself by tearing apart a piece of junk

    I started this project with another post involving me, a crackerbox $30 mandolin and a superglued bridge. Now that the bridge (and a hunk of finish) are off, I'm trying to figure out how to remove the finish down to bear wood.

    Now, I know from many, many other posts that the general opinion is that you don't do this. But I want to learn how to do it when I don't have to, so I will know how to do it when I do have to.

    The finish is a very thick, plasticky layer. What it is I don't know, but given the cheapness of the instrument and the thickness and shine it's got to be poly-plastic-something or other.

    Question one: How do I identify the finish?

    Question two: how do I get this crap off? Someone suggested that I try mineral spirits, which had no effect at all. So, what now? Acetone? Xylene? Chemical stripper? Heat gun?

    Thanks in advance for all of your input.

  2. #2
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    Default Re: Teaching myself by tearing apart a piece of junk

    Polyester and polyurethane plastic finishes are remarkably resistant to solvents and chemical strippers. Physical removal is the best alternative. Sanding it off is a heck of a lot of work and makes a lot of dust. This Stew-Mac newsletter proposes using a heat gun to soften the finish then scrape it off. Here is a link for the procedure:
    http://www.stewmac.com/tsarchive/ts0151.html

    For what it's worth, anyone getting started in lutherie or just having an interest in the topic, Stew Mac has a ton of FREE information on their web site. Sure, a lot of it has to do with guitars but a lot of it is applicable to any kind of string instrument. Plus...did I mention it's FREE?
    Don

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  3. #3
    Registered User sunburst's Avatar
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    Default Re: Teaching myself by tearing apart a piece of junk

    Multidon is right; forget chemicals for stripping a poly finish. I'd use a sharp scraper or two and scrape it down 'til the wood starts to be exposed in a few places, then sand away the rest. It will make a mess, but it's about all you can do, and scraping makes less breathable dust than sanding, and we don't like to breathe dust.

  4. #4

    Default Re: Teaching myself by tearing apart a piece of junk

    Mineral spirits is not much of a test since it won't dissolve many finishes once cured. I think before you commit to scraping you should test it with a few other solvents unless you are absolutely positive it is a polyester finish. Try alcohol and lacquer thinner. You might even try a chemical stripper. If none of them do anything then go for scrapers. Those poly finishes are tough. My first mandolin was an inexpensive import and I decided to refinish the back. I took my random orbital sander to it and all I managed to do was take the sheen off of it. At that point I decided I did not want to refinish after all.
    Bill Snyder
    Vintage Tools, etc

  5. #5
    Registered User EarlG's Avatar
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    Default Re: Teaching myself by tearing apart a piece of junk

    Go to Home Depot and get the "Citristrip" paint remover. It will take it right off and it seems relatively safer than other paint strippers. Get some of the Scotchbrite type scrubbing pads in case your finish is extra tough the stripper pad helps. I did this with a Cremona fiddle, although I am not sure the shiny finish was poly. It was sure thick and shined a lot.

    If you don't want to use the chemicals, scrapers (woodworking scrapers, not paint scrapers) will work fine as well, slower but much less mess.

  6. #6
    Registered User belbein's Avatar
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    Default Re: Teaching myself by tearing apart a piece of junk

    Thanks, everyone. I will try a chemical stripper, just to see what happens. Then I'm going for heat. If the heat fails, then there's always my belt sander--with which I'm pretty handy--and if not that, then there's always the grinder I use for fiberglass. (I think I'm kidding with that last. Depends how frustrated I get.)

  7. #7
    Registered User Tavy's Avatar
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    Default Re: Teaching myself by tearing apart a piece of junk

    Heat isn't a good idea - very likely the glued joints will give way before the finish

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