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Thread: Martin Mando Finish Repair Q

  1. #1

    Default Martin Mando Finish Repair Q

    Hi

    I have a 50s Martin Style A with a nasty sticker scar. What to do?
    Seems like I'll need to mix up some shellac and fill the divots..then what?
    I am not an experienced instrument finisher, but I'm not afraid of fine brush work. (ex-old school photo retoucher)
    What are your thoughts? Useful links, YT vids, advice welcome..
    thanks

    Peter

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  2. #2
    Registered User sunburst's Avatar
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    Default Re: Martin Mando Finish Repair Q

    By divots, do you mean little places where the finish was removed by the act of removing the sticker? (I can't quite tell from the picture.) If so, drop filling with lacquer would be a good procedure for repair.
    In the 50s martin was using nitrocellulose lacquer for finish, so that is the material to use for repair.
    I keep a small bottle of lacquer that is evaporated down to about the consistency of honey. Drop in a small amount with a small brush, let it dry and repeat until each void is completely filled. Let the repair cure for at least a couple of weeks and level the surface, sand to probably 1200 or 1500 grit sandpaper and rub with some kind of compound until the gloss matches the surrounding finish as closely as possible. If you have or want to get Micromesh, usually around 8000 grit will match an old Martin finish. The repaired area will look much more level and will look newer than the surrounding old surface, but the difference will moderate over time.
    It may be that you need to use lacquer with some amber color added to get the fills to match the old lacquer. It sort of depends on how deep the damage it.
    Last edited by sunburst; Nov-29-2018 at 11:20pm.

  3. #3

    Default Re: Martin Mando Finish Repair Q

    John,
    That is exactly the info I needed, and confirms what I gleaned from my internet wanderings. Yes, finish was pulled off in small flakes along with the sticker. .
    You seem to recommend a very thick solution..hmm I'll have to experiment, I found a source for dry lacquer locally already..
    After curing, I should level how? I saw a video with a taped off single edge razor, but that person was using CA.
    Also "lacquer with some amber color": does that mean buy lacquer of a certain tone, or use colorants (watercolor tint, for ex) to tint it?
    I do think it will need some color, as the overall finish is moderately age darkened.
    I know I am unlikely to do a perfect job on this, but I mostly want to keep the divots from becoming dirt pits, if I can make them disappear, that will feel like I've gained a superpower. Thanks for your helpful comment.
    Peter

  4. #4
    Registered User sunburst's Avatar
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    Default Re: Martin Mando Finish Repair Q

    Some people tape the edges of a razor blade and scrape touch-ups level, I only do that sometimes. usually, I just use an exacto blade and magnifying visors and use side lighting and practiced dexterity to scrape level. After that, gentle block sanding. This may seem obvious, but be sure to not scrape too deep. It can be darned disappointing to start level sanding and find that you've created a new divot where one was just repaired (DAMHIKT).
    For color, if you need it, it must be something compatible with lacquer. I'm pretty sure you can't buy lacquer that will match. Many of us keep a bottle or two of very old lacquer around. It becomes darker and darker in color as it ages. It's a pretty sure bet you haven't done that, so adding some amber color to new lacquer is probably what you'll need to do. Try a little lacquer in one or two of the divots first though, the color might look fine. I have my doubts that watercolor tint will be compatible, but I don't know for sure. (water is a polar solvent and lacquer thinners and reducers are non-polar) Try a little and see if it mixes. If not, there are various lacquer tinting dyes available. Aniline dues, metal complex dyes, etc.
    Leaving the lid loose on a bottle of lacquer will allow solvents to evaporate and the lacquer to thicken. Filling with thickened lacquer speeds up the process, but lacquer as supplied will work too, just more slowly.

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  6. #5
    Registered User Greg Mirken's Avatar
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    Default Re: Martin Mando Finish Repair Q

    Some other tips to keep in mind- work in as small an area as you can to avoid messing up the wonderful patina the top has acquired. Polish, for example, will get into those tiny checks and look bad. Also, test your drop-fill in one small pit first. Often the wood will suck up lacquer and look darker than the surrounding surface. If so, thin some regular Titebond with water [ more water than glue] and paint the bare spots to seal the wood. Wait a day and try another spot.
    You can't make them disappear. Aim for tidy and inconspicuous.
    Shade Tree Fretted Instrument Repair
    Now located in Nevada City, California
    http://www.shadetreeguitars.com

  7. #6

    Default Re: Martin Mando Finish Repair Q

    Thank you Greg. More great tips.
    I post my noob question, and two seasoned pros give me concise and friendly advice with no bluster or attitude.
    Thanks to you both for the excellent info, and yay for the forum!

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