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Thread: Need suggestion on removing bad finish from a build.

  1. #1

    Default Need suggestion on removing bad finish from a build.

    I mentioned briefly in another thread a build I'm currently working on, an IV kit, which is my first mandolin build. I'm not a first time instrument builder, but this build has had tons of firsts for me.

    On to my problem- I'm currently laying a lacquer finish on the instrument and unfortunately, I just got the news that I've sprayed the instrument with 8 coats of really nice lacquer that is not and will not dry. It is gummy and near greasy to the touch.

    The tech person at the vendor has suggested either removing the finish with lacquer thinner or sanding it off.

    I did my first sunburst finish using aniline dye on the instrument and it has celluloid bindings. That makes me think using lacquer to remove the finish is a terribly bad idea.

    I've tried sanding it lightly, and the finish literally rolls up in balls on the sandpaper in most places. Some places it just forms up a gummy sludge.

    Anyone have an appropriate suggestion?

    I've played the instrument in the white, and its one of the better sounding mandolins I've played (and of course I'm proud of it!). I really don't want to ruin this one

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    Chinn A-style
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  2. #2

    Default Re: Need suggestion on removing bad finish from a build.

    I've stripped back with lacquer thinner before. You can scrape the bindings first then brush shellac on them then strip with lacquer thinner. The thinner won effect the shellac. Once most of it is off then you can sand or scrape the residual. I always seal with shellac so when I spray my bursts I can strip them back if I mess them up.

  3. #3

    Default Re: Need suggestion on removing bad finish from a build.

    I had always heard it takes a year to 15 months for nitrocellulose lacquer to cure........

    I saw on a forum where someone half-jokingly said it takes "six months to never" to cure.......

  4. #4

    Default Re: Need suggestion on removing bad finish from a build.

    What reason did someone say it wont dry? Did you have a two part lacquer that you didn't catalyze?

  5. #5
    Registered User fscotte's Avatar
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    Default Re: Need suggestion on removing bad finish from a build.

    I'd give it more time. If it's only been a week, give it another week.

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  7. #6

    Default Re: Need suggestion on removing bad finish from a build.

    Thanks for the suggestions everyone. I may do a test piece with some shellac to make sure I have an idea what I'm doing.

    The confirmation it would not cure came directly from the manufacturer of the lacquer, based on the lot number on the can.

  8. #7
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    Default Re: Need suggestion on removing bad finish from a build.

    You can mask the bindings while the rest of the instrument is being stripped.
    You might start out dry, and carefully try some coarse steel or plastic wool or even a coarsely sharpened cabinet scraper to take the upper layers off, or even start with some 150 or 180 sandpaper. Then finish up with scraper and/or 220 and 320 sandpaper.

    I have successfully used solvents such as lacquer thinner or denatured alcohol along with a cabinet scraper to remove soft nitro and shellac, but the solvents tend to drive some of the finish deeper into the wood pores. This may disrupt your chances of getting a new, clean surface without working your plates too thin.

    My suggestion would be that if you use solvents, use them only to get rid of the upper layers, then finish off by stripping the remainder mechanically. I'd start with alcohol instead of thinner, it's a little less toxic. If it doesn't work, then you can try the thinner. Work outside, and wear a mask.

    If the manufacturer says the stuff is no good, there is no reason to wait around and hope it will cure.

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    Chinn 

  10. #8
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    Default Re: Need suggestion on removing bad finish from a build.

    Is this nitro? Were the first 7 coats dry before you sprayed on another coat?
    What's the brand of finish? This sounds really odd.

  11. #9
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    Default Re: Need suggestion on removing bad finish from a build.

    Never mind my last post. I just read your post on the other thread. I've used Mohawk Instrument Lacquer for years. The "too much plasticizer" would act like that.
    I'd scrape as much off as possible without harming the wood. Then probably lacquer thinner, coarse steel wool, Don't let it sit on long. And no straight acetone- that will attack the bindings quickly. And while stripping, I'd stop regularly and let it dry with lots of ventilation and a fan. This is to dry the binding regularly.
    Some of us have been here before.

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  13. #10
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    Default Re: Need suggestion on removing bad finish from a build.

    my last build kind of stayed tacky for what seemed like way too long. i took it into the the air conditioned bedroom where the air was less humid, and in a couple days she dried

  14. #11
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    Default Re: Need suggestion on removing bad finish from a build.

    I have nothing useful from a technique standpoint, but would like to thank the luthiers who have responded for their generosity with their knowledge! Also, to the OP, best wishes. It must be tough to be so close and then have to take this unexpected step...
    Chuck

  15. #12

    Default Re: Need suggestion on removing bad finish from a build.

    Thanks again for the feedback everyone. I ended up using a combination of techniques to get the job done.

    I started off using scrapers to remove the majority of the finish. This worked in most areas really well. The finish came off roughly in the consistency of a skim of strawberry jam that's been left on a plate for a few days -if you have or have had teenage kids or a bad roommate, you can imagine what I'm speaking of.

    I then turned to a combination of pretty heavy sandpaper and steel wool for a few difficult to reach areas.

    Finally, I taped off the bindings and carefully wiped down the remainder with straight lacquer thinner.

    I'm going to re-finish-sand the mandolin to eliminate any of the marks from removal - thankfully there really are not many - and then go back to finishing again. The vendor has shipped a new batch of lacquer and I should have that shortly.

    Regarding the question of if the finish was dry between coats- I've used this lacquer before, so I waited the amount of time I normally do between coats and shot the next. I did touch the finish on a taped off area, and on the first few coats, it felt fine. After about the 4th coat, it started to feel almost greasy or waxy. I was not sure if I had a humidity problem or what at that point. When I felt it a few days later and it was the same, and I could fingerprint the taped areas very easily, I knew I had a problem. I've refinished/painted vintage cars, motorcycles and boat motors for many years. I also do another woodworking hobby in which I finish 75-100 pieces a year with varying finishes (I'm a game call maker). Everything in my experience told me I was in trouble.....
    Chinn A-style
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  16. #13
    Registered User fscotte's Avatar
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    Default Re: Need suggestion on removing bad finish from a build.

    You never mentioned, but careful how and what you use to clean your spray gun with. I've made the mistake of not using clean "cleaner" to clean my gun with. The residue from the cleaner mixed in with the lacquer and created issues that had to be fixed.

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