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Thread: Cleaning gunk off a nitrocellulose lacquer finish

  1. #1
    Martin Stillion mrmando's Avatar
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    Default Cleaning gunk off a nitrocellulose lacquer finish

    Electric mandolin arrived from Europe today. Some Philistine previous owner had glued a couple of strips of rattlesnake skin along the sides and added some butterfly decals. I managed to reach the builder, Kevin Parsons of Newcastle-on-Tyne, and he practically begged me to remove all that stuff, which I now have. (The wife wanted to know how snakeskin got in the wastebasket.)

    There is an awful lot of gunk left behind, however. Kevin says he only ever used old-school nitrocellulose lacquer finishes, and I should use what are called 'white spirits' in the UK if I needed help with gunk removal. He thinks that's the same stuff as what is called mineral spirits in the U.S. I have plenty of mineral spirits.

    Should it be OK to use some mineral spirits on a soft cloth with this finish, if warm water alone doesn't do the trick?
    Last edited by mrmando; Apr-19-2021 at 8:48pm.
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    If it is indeed nitro, yes. I would use mineral spirits before I would use water. It may need several applications. Apply, let it soak into the goo or glue or whatever it is for a little while, wipe carefully with a clean rag. When the rag starts loading up, move to a fresh section of the rag. Repeat as necessary. Avoid aggressive rubbing-- particles from whatever is on it will scratch the finish below. Final cleaning can be done with extra fine compound or swirl remover, if the remaining finish is not too thin. If it's very thin, use rottenstone and mineral oil.

    If the goo will not soften, it will have to be removed mechanically by an expert.

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    Registered User sunburst's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    If I don't know what the "gunk" is I start with water. Just a damp, soft cloth, not a garden hose. If nothing happens, add a little detergent or soap. If nothing happens, naphtha. If naphtha does nothing, physical removal comes next.
    If, in this case, the gunk is known to be some sort of contact adhesive that is not water soluble, I'd start with naphtha.

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    Martin Stillion mrmando's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    Isn't naphtha precisely the wrong thing for nitro finishes, though? I have both, but Kevin warned me to stay away from the naphtha.
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    I have never known of finish damage to nitro from naphtha. But if the builder warned you away from it, he may have a good reason.
    Maybe what they sell as naphtha in the UK is different than what they sell in the US? I don't know. Or maybe his nitro is different-- nitro formulas vary considerably.

    Idea: why don't you remove one of the tuner strips and do a test in that area with some naphtha on a q-tip?

    I know that both naphtha and mineral spirits will soften many of the contact adhesives enough that they can be wiped off. I usually just dab some directly on the adhesive, wait, then wipe. Naphtha evaporates much more quickly. Usually, that's a good thing. If you get a successful test, I would try it first. Sometimes the slower evaporation of mineral spirits can be useful to allow more time to soften the goo. But if there's deep checking, there's a chance that mineral spirits may sink into the checks and darken them. I've never known either of them to dissolve nitro, at least not US products.

    But: Even though cleaning a dirty finish sounds like a simple, safe job, it's not. It's easy to end up with a scratched finish or bare wood even if you're really careful, especially on old finishes.

    I'm always really careful about using water, especially on old finishes. In my experience, I've sometimes had scratching problems, and on a really dirty, thin old finish, using water has sometimes resulted in exposure of bare wood. An old time cabinet maker friend of mine considers it to be an enemy of lacquer, and in at least some cases, I concur. I do use it from time to time, but sometimes I cross my fingers. Filtered water is better than tap water, but the next time I feel the need to use it, I'm going to use distilled water.

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    Martin Stillion mrmando's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    Thanks for all the advice. I'm not sure when I'll have a block of time to get started on this, but I'll check back in with the results.

    Trying to learn to do a little more setup and repair work, although I will probably also continue to collect projects to delight my favorite luthiers.
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    Still a mandolin fighter Mandophyte's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    In the UK naphtha is available as lighter fuel.
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    Naphtha should be fine. Acetone is the thing to avoid, as it will burn right through nitro.

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    Registered User sunburst's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    Quote Originally Posted by mrmando View Post
    Isn't naphtha precisely the wrong thing for nitro finishes, though? I have both, but Kevin warned me to stay away from the naphtha.
    I've never experienced nor heard of naphtha damaging nitro finishes. I don't know what the builder's application technique was or if he did something different to the surface, so he might have a reason for warning against naphtha, but I suspect it would be safe.

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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    I believe naptha and mineral spirits are essentially the same thing.

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    Registered User j. condino's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    Plenty of the new formulas sold as nitro are not the same durable thing from days gone by. The current Cardinal "nitro" lacquer blushes from alcohol three years later....

    A tip for removing old bass rosin and similar gunk: Take an old credit card and burnish it like a scraper to form an edge with a burr; use that to scrape off most of the old gunk first, then go with your chemical of choice...

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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    When the nature of the gunk is not known, it will be an experiment to discover what removes it. You need to know first what the underlying finish is, so you have some clues about what cleaning agents to ovoid. Nitrocellulose lacquer is pretty tolerant to solvents that are not what I would call "hot". Acetone being the most hot followed by lacquer thinner. Alcohol, Ammonia and Turpentine fall somewhere in the middle. Naphtha and mineral spirits being the least hot of any of the solvents I might typically use, and of course water. Gunk can be water soluble, oil based and need a solvent, or a combination of both. If neither of those approaches gets the job done, it's mechanical removal.

    For Nitrocellulose lacquer, Acetone and Lacquer thinner will dissolve the finish outright and should not be used. Alcohol can soften lacquer but can be used sparingly for things like blush removal. Ammonia should never be used full strength. A small amount mixed with water though can be a very effective gunk remover. Use sparingly, follow up with a water dampened cloth and then a dry cloth. Ammonia will dissolve varnish finishes! I have found that Turpentine does not seem to soften lacquer and sometimes use it sparingly when Naphtha doesn't quite get the job done. I may also use it on on instruments that have been exposed to a lot of cigarette smoke, helps with the odor. Naphtha is very good for removing tape or sticker adhesive residue. Naphtha is my main go to solvent as it is also proven to be varnish safe, at least I can say that I have never had a problem with it. I also like Naphtha because it evaporates completely, very quickly and does not leave any residue on or under checked finishes. Naphtha and Mineral Spirits are not the same. White Gas and Goof off are in the Naphtha family. Goof Off has other additives and I have no reason to experiment with White Gas. Mineral Spirits can vary quite a bit in its formula and I don't like the oily feel or the amount of time it takes for it to evaporate, I won't use it for anything but cleaning brushes.

    Water is an excellent solvent by itself or with a bit of detergent added. De-ionized water, if you can get it, works best. As Sunburst eloquently puts it "you don't need to get the garden hose out". It's more like the line from Karate Kid "wax on, wax off". Apply sparingly, dry immediately.

    Of course it is recommended to check any solvents compatibility or not with a finish by removing a tuner or tailpiece and trying it out where it will be covered.
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    ... And, along with all other precautions, when wiping a finish by hand, always wipe with the wood's grain. Micro scratches happen no matter what kind of cloth is used, so may as well make those micro-scratches follow the grain (and also most likely any previous hand rub-out work).

    Also, if the finish is a "satin" finish, be aware that any wiping will tend to "gloss" the area that is wiped.
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    Martin Stillion mrmando's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    Well, neither the mineral spirits nor the naphtha damaged the finish in the test area. Mineral spirits did bugger-all to soften the gunk, but the naphtha is doing the trick.

    Came across what looked like a piece of tape ... maybe it was double-sided tape that originally held the snakeskin on the instrument? Hm.
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    I've found that BOSS Guitar Detailer takes a lot of funky goo off instrument finishes - even that weird haze that forms on instruments left in the case for decades.

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    The Amateur Mandolinist Mark Gunter's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    Can naphtha damage a nitrocellulose finish? The answer is yes, it can if you are careless with it. If naphtha fumes get trapped for any length of time on a nitrocellulose finish it will indeed damage a nitrocellulose finish. Never allow a rag that has been used with naphtha to remain in contact with a nitrocellulose finish for any length of time (an hour or more). I have known naphtha rags to damage cured nitrocellulose finishes a few times over 30 years of finishing experience through carelessness ... and just want to chime in to clear up that misconception and to say don't be careless with shop rags.

    My preference for cleaning adhesives and such from a cured nitrocellulose finish is naphtha, it can be used even in abundance without harming the finish as long as it is wiped dry and allowed to evaporate freely. Practically any solvent can damage a nitrocellulose finish as it evaporates if it gets trapped (by a rag for instance). This is the same type of slow process that causes certain plastics and rubbers to damage nitrocellulose finishes when in contact over long periods, so be careful.
    Last edited by Mark Gunter; May-19-2021 at 7:47am. Reason: word choice
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    Registered User BBarton's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    This thread is all about nitrocellulose finishes, but will naptha clean dried "gunk" from a satin finish? If not, other suggestions?
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    Registered User sunburst's Avatar
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    Default Re: Cleaning gunk off a nitrocellulose lacquer finish

    "Nitrocellulose" and and "satin" are not mutually exclusive. In other words, a "satin" finish can be nitro or it can be nearly any other finish material.
    Naphtha, used in moderation, is generally safe for any common finish material. As always, test in an inconspicuous place and/or check with the maker/manufacturer of the instrument to see what the finish is.

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