Need tips on retouching

Discussion in 'Finely Finished' started by mdossa, Jun 24, 2021.

  1. mdossa

    mdossa TDPRI Member

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    I'm new to guitar finishing works, so please bare with me. I did some retouching on this guitar where the black paint was badly scratched, then applied a clear nitro coating over the area. It looked OK at that point, apart from the obvious level difference of the new coat. Wet-sanded the area down with 400, 600, 800 and 1200 grit, then buffed and polished by hand. The result is frustrating. My questions to you guys:
    a couple of areas now show a kind of blur, like a difference in brightness. It won't go away with polishing, so I take it it lies deep below the nitro coat. Could it be a different kind of finishing there? Or something to do with humidity? And what about the fine ring shaped scratches that still show after polishing, is it possible to get rid of those? Thanks a lot for any insights!

    IMG_20210624_092308369.jpg
     
  2. Preacher

    Preacher Friend of Leo's

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    Ok we need a few more questions answered.

    First off, what kind of finish is on the original guitar? This is really important because if the original finish is not nitro spraying nitro over the old finish is a bad idea.
     
  3. mdossa

    mdossa TDPRI Member

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    That's where I'm stumbling. I suspect it may not be nitro, but how can I find out what is in the old finish?
     
  4. dogmeat

    dogmeat Friend of Leo's

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    that can happen even when using the same finish, out of the same can. nitro on nitro is easier to get away with because the new literally melts into the old. any kind of acrylic, poly, or enamel paint is going to show that layered effect to some degree. the cure for what you have is to coat the whole thing, clear or color.

    now, you can do drop fills... go over to StewMac and look at Dan's how to
     
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  5. Preacher

    Preacher Friend of Leo's

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    Make and model of the guitar will help.

    My guess, it is a poly finish and spraying nitro over the top of it won't do anything for you other than leave a hazy finish on top of the poly.
    Nitro will not blend into the poly like it would into Nitro.

    Working on that assumption, to do touch up on poly guitar is not that hard.

    Here are the steps I take to do a fill/touch up on poly.

    1) find some finger nail polish that matches the color of the fill.
    2) using some clear office tape, place some tape around the area you want to fill. This will give you a dam to allow the polish to fill above the surface of the guitar.
    3) fill the divot, gap or mar with the polish. It might take a couple of passes to fill the issue depending on the depth of the problem.
    4) once you have the mar filled and flowing up to the top of the tape let it dry completely.
    5) remove the tape and then using a razor blade scrape away the excess fill on top of the surface. If the dent is on a radius this gets a little tricky. One thing you can do is create another dam with the tape and use that to keep the blade from scrapping too deep.
    6) Once you get the excess scraped ALMOST to the finished surface, then you can go to the sand paper.
    7) do the sanding like you did before, 400, 600, 800, 1200, 1500 and 2000 (I know you did not mention these last two but they are essential to get the swirl marks out that you currently have). Change your paper frequently as the paint builds up and can cause more scratches than the sand paper.
    8) now you turn to buffing. To get a high sheen it is going to require a high speed buffer to get the results you want. You can only go so far with hand buffing. I do prefer hand buffed finishes (personal preference) but if you want to see your face shining in it by morning a high speed buffer (even a drill unit will suffice) is the tool for the job.
    9) it may take a few passes to get the fill where you want it. Sometimes the polish will shrink a bit as it cures. Just redo the steps again until it is satisfactory.

    The other option is to allow it to naturally relic. I find this to be the best option!
     
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  6. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    Exactly what Preacher just said - lacquer will melt into previous coats of lacquer, one of its real advantages. Lacquer will NOT melt into any of the modern catalyzed poly-something finishes. In fact, nothing will. I've pretty much given up trying and tell folks when I do repairs that they will not be cosmetically perfect. In fact, on many new guitars I just don't try.

    btw - if you don't know how to test, pull one of the tuners off and put a drop of lacquer thinner on the footprint. If the finish softens its lacquer, if not its something else.
     
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  7. mdossa

    mdossa TDPRI Member

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    So it looks like we're getting to a consensus that it should be a different finishing there. Will use your tips to check that, then perhaps try to remove the nitro layer. Absolutely appreciate your input, guys.
     
  8. Reua95

    Reua95 TDPRI Member

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    I used Starbond Black CA glue to repair a bad gash in the finish MIM telecaster body. Worked pretty well for me.
     
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  9. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    That might be harder than you think too. Maybe best to just leave it.

    I'll add one comment to Preacher's discussion - finger nail polishes are usually lacquer based. Drop filling with finger nail polish on lacquer works very well because just like lacquer itself there will be some burn in. I've never tried drop filling lacquer on poly finishes but I would expect to react just like spraying nitro - poor adhesion, probably look pretty bad.

    I have had reasonably good luck drop filling poly finishes with colored medium CA. I really like a product called Gluboost, their instructions on drop fill are some of the best. The CA will not melt into the poly but is cures hard enough to do all the steps Preacher describes.

    I'm not sure I would drop fill your dings however, I'm just not convinced I could do anything that would make it look better
     
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  10. Preacher

    Preacher Friend of Leo's

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    @Freeman Keller is correct, finger nail polish for nitro finishes. Testers model paint is usually poly paint.
     
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  11. telepraise

    telepraise Tele-Afflicted

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    It looks pretty good as is to me. Black gloss is THE toughest finish to get flawless. How bad does it look without a bright light shining on it?

    If the original finish is a synthetic (highly likely) it will be impossible to get an invisible color patch without witness lines, no matter how fine you sand (believe me, I've tried). Picture sanding a bevel on a piece of plywood where each ply is a coat/layer of finish. The bevel edge is going to show through the patch finish at least a little.

    The ring shaped scratches are the result of not enough time with the finer grits. The stinker is that those scratches are almost impossible to see until you buff it out, especially with black. Again, I'd call it close enough.
     
  12. eallen

    eallen Friend of Leo's

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    Witness shadows. I have also seen nitro on nitro have shadows in certain instances for unknown reasons.

    I would also add, sanding a finish with 400 is a sure recipie to get scratch Mark's that won't come out or a sanded thru finish. You could have sanded thru some color. I never use anything finer than 800.
     
  13. mdossa

    mdossa TDPRI Member

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    I don't have any illusions at this point, I'm sure it won't be easy. Good advice on CA also, though I don't think it would help me on this particular case.

    Not so bad actually. I had to try and find the best (worst) angle to make it show in the picture. I'm sure nobody wil notice it when I'm playing in a dimly lit pub. :D But I'm trying to learn more on finishings and all the dos and don'ts.
     
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