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Thread: Finish issues

  1. #1
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    Default Finish issues

    I have been having issues trying to finish one of my GOM's. Some (probably all) of it is my own lack of skill where there were gaps in the binding that had to be filled, but these 2 issues I cannot explain and am looking for insight to the causes. I have attached 3 photos. 2 show an issue with the lacquer adhering to the ebony. When I pressed in the tuner grommets the lacquer lifted from the ebony around them. When I laid the strings next to the neck to work on the bridge chips came off of the edges as shown in one of the pictures. Just bumping the binding started to lift the finish as in the other picture. The issue also came up when I removed the tape from the fretboard. It chipped in several places along the ebony edge. I have touched up and repaired most of it but would like to know the cause to avoid a repeat.
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    The other picture shows a discoloration in the quilting that when looking at it in normal light it makes the finish look worn, but the finish itself has a good polish. The issue is below the lacquer in the coloration in the quilting. I did not notice this before I applied the nitro, and I suspect anything I do to try to repair it will just make it worse. Has anyone seen this issue before?
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    I did put a light coat of 1lb shellac on the instrument before I started the nitro applications, but I noticed that when I level sanded every 4 coats the swill contained a bit of color and by the time I was finished the instrument was a bit lighter then when I started.
    Bob Schmidt

  2. #2
    Registered User sunburst's Avatar
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    Default Re: Finish issues

    Can you outline your procedure from sanding through buffing? How was the shellac applied and how soon after staining? How soon after final sanding was the dye applied? Was the color rubbed? Sprayed? Other? What is the color? Dye in alcohol? Dye in water? Other?
    Lacquer does not adhere to ebony as well as many other woods, but it looks like the finish chip in your second picture involves the maple as well so there might be some incompatibility somewhere or some problem in the process..

    I don't think I am seeing what you are trying to show in the last photo.

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  4. #3
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    Default Re: Finish issues

    Finishing is not my strong suit, but I'll mention that probably 50% of finishing problems are due to not waiting long enough between steps. And it probably doesn't hurt to double the drying time between steps when working with colors.

    It's probably a good idea to wash down both ebony and rosewood with naphtha before applying any finish.

    Don Teeter mentioned in his now ancient book on guitar repair recommended that Indian rosewood be washed with naphtha, followed by lacquer thinner, followed by alcohol. You might try that on a piece of ebony scrap and see if it yields better results.

    Oh-- how old is your shellac, and did you filter it? Shellac mixed with alcohol can "pickle" in as little as 30 days after it is mixed, though sometimes it's good for 3 months. After that, it should be discarded. Also, the dry shellac flakes have a shelf life too. A rule of thumb is if it does not completely dissolve overnight when mixed in alcohol, the flakes should be discarded.

    I see color variations in your quilting that appear to be dependent on the "depth" of the quilt, and some "quilt pockets" that are lighter or darker than others. I would think that at least some of this is simply the character of the wood itself. If you are staining the wood itself, it may accentuate the color differences. If you are looking for more even coloration, you might want to confine the color only to the base coats that are applied after sealing.

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  6. #4
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    Default Re: Finish issues

    John, rcc
    I will try to hit all of the questions. The shellack was a fresh mix and it did dissolve overnight although it was stirred a few times while I was out in the shop to break up the larger pieces. The flakes are around a year old and are double sealed in plastic bags.
    The quilting and top color was dye and everclear. I applied black first then the red tone mix after sanding to bring out the grain. That was all done only waiting for the alcohol to dry. The back and side coloring was rubbed on. The top color was applied with an airbrush, but other then getting lighter with sucessive color sandings I have had no issues with it.
    I then rubbed a light 1lb cut of shellac on the entire instrument, again only after the stain was dry. I did not sand afterwards, perhaps that was a mistake?
    The nitro was applied with my full size devilbiss gun. I applied 3 to four coats per day and let it dry overnight. I would color sand with 600 paper to level the finish each day before the next coats. There were sometimes more then one day between this process depending on the weather and time i had, but that was the general procedure I used.
    I used a similar procedure with a second GOM that only had a light coloring on the back and sides. The bindings there are bloodwood. The only ebony is the fingerboard, but I have had no issues with it.

    The chip did go slightly into the maple when I popped it off but it did not continue to spread like it did in the ebony. I finally got so annoyed with the chipping that I took the headstock down to bare wood, washed it with lacquer thinner and sprayed it directly with lacquer, no sealer and that seems to be working.

    Taking a closer look at the back I do see similar but not as pronounced color variations in other parts of the back so perhaps it is just in the way the dye took to the wood. I will have to look more carefully before finishing next time.
    Bob Schmidt

  7. #5
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    Default Re: Finish issues

    It sounds like cleaning the ebony with lacquer finish might have solved your problem.

    Lifting finish from tuner bushings is a common problem. I've seen it on loads of modern Gibson and Martin instruments. Both companies tend to lacquer heavily and quickly, and that certainly doesn't help. Another possible cause is finish drying too quickly, causing a poor bond between finish and wood, or between a new coat and the coats below it. Some folks use just a little bit of lacquer retarder in hot and/or humid weather.

    Anyway, I hope that you've got it solved. It might just have been caused by gremlins hanging around with nothing else to do. They were busy in my shop in February.

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  9. #6
    Registered User sunburst's Avatar
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    Default Re: Finish issues

    A couple of things I suspect:

    4 coats of lacquer in a session is a lot. Most of the lacquers that I have used recommend 2 coats in a session, but I usually cheat a little and spray 3. It is important for each coat to flash off completely before applying the next, and that goes much more quickly with 2 coats than with 3 (or 4). That might be part of the problem.

    It has been said and written many times and many places that wiping with a solvent helps adhesion of finishes over difficult, oily or resinous woods. The more scientifically oriented approach is to apply glue or finish quickly after refreshing the surface by removing the surface wood (sand, scrape, cut...). That means sanding ebony or bloodwood or rosewood or whatever soon before applying finish. For gluing, the rule of thumb is to resurface (sand, scrape, cut) rosewood within 15 minutes of gluing. I think the same will help adhesion of finishes.

    I suspect sanding your shellac would have helped the situation.

    (If you want to read up on the reasoning behind a fresh surface being better for adhesion there are explanations in various places on the internet. I think I might have offered a brief explanation somewhere on this board in the past.)

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  11. #7
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    Default Re: Finish issues

    So far so good. The strings are on it and no new issues. If the bindings start to chip I may have to scrape them clean and respray them. This one has been a struggle but since it is the first one I have tried color on it has taught me a lot. If it did not sound so good it may have wound up looking like John Condino's avatar.
    Thanks for the feedback. I will be more careful and patient with the next one.
    Bob Schmidt

  12. #8
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    Default Re: Finish issues

    What brand of lacquer did you use? Shellac has a reputation as a universal sealer, but there are some incompatibilities, so you have to be a bit careful with it. I assume it was dewaxed shellac that yo used?

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  14. #9
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    Default Re: Finish issues

    The lacquer was the colortone guitar lacquer sold by StewMac. I bought the shellac from LMI, and was not aware that there was a difference, but I will check when I get back in the shop.
    Bob Schmidt

  15. #10
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    Default Re: Finish issues

    I expect that if you got it from LMI the shellac is dewaxed, which is what you want for a sealer coat. I believe shellac should be okay as a light coat under the Colortone lacquer, but it can cause major problems under Cardinal lacquer. I think vinyl sealer has gotten a bad name (partly because of confusion with sanding sealer), but I have found a light coat of vinyl sealer to be indistinguishable from a shellac seal coat, and I get very good adhesion with it.

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