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Thread: How to remove unidentified old glue

  1. #1

    Default How to remove unidentified old glue

    I was recently brought this Gibson headstock break and upon examination, discovered that it was actually a re-break. The owner doesn't know who did the first fix but there's enough old glue left that I removed chunks, and tried dissolving them in hot water, vinegar & acetone. No luck. It's amber in color, and the build-up in the trussrod cavity is thick enough that I suspect it may be epoxy.Click image for larger version. 

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    I'm afraid to reglue without removing the old, failed glue, but not sure how to best remove it. Any suggestions?

    Neil

  2. #2

    Default Re: How to remove unidentified old glue

    I've got some metal dental tools that I use to pick the old glue out of there. Kind of like a small awl. Get a good light, wear a magnifer, and take your time. I don't know how much more "flex" you have, but if you can open it wider, you might be able to get the little wire brush wheel in their with your Dremel -- might be faster. Get as much of it out of there as you can and reglue. Good luck!

  3. #3
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    Default Re: How to remove unidentified old glue

    Maybe a hand held hair drier or some steam to heat up the glue might help. I have some dental picks also, mine are the angled scraper with a point to very helpful in these cases.
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  4. #4

    Default Re: How to remove unidentified old glue

    I do have some dental picks to take off larger chunk, but I'm concerned about the thinner residue covering most of the surface. Are you saying you scratch away at the entire surface? What kind of glue would you use after cleaning things up?

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    Café habitué Paul Hostetter's Avatar
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    Default Re: How to remove unidentified old glue

    I'd recommend a steam needle (like is used to remove guitar necks) to get the old glue completely out of the grain of the wood. Then let the wood dry real well, and reglue using HHG or a good aliphatic.

    It's possible to use acetic acid, white vinegar, and some products containing same to break down the glue, but you then still have to clean that out of the pores to neutralize the pH so new glue will actually adhere. I'd skip the acetic treatment and just use a steam needle and a toothbrush.

    You can't get enough out with dental picks, though you can get rid of some of the larger chunks that way.
    .
    ph

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    Default Re: How to remove unidentified old glue

    You know looking closely at your picture I was entertaining the thought that you might be dealing with a polyurethane glue like Gorilla glue? Not sure that would be good news as only physical pressure seems to remove it (e.g., scraping).
    Bernie
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    Café habitué Paul Hostetter's Avatar
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    Default Re: How to remove unidentified old glue

    Quote Originally Posted by Bernie Daniel View Post
    You know looking closely at your picture I was entertaining the thought that you might be dealing with a polyurethane glue like Gorilla glue? Not sure that would be good news as only physical pressure seems to remove it (e.g., scraping).
    This video is barely applicable. If the headstock in question was once glued with Gorilla glue, scraping and sanding are simply out of the question. You need to clean all the glue out of the pores of the wood to be able to start over. In this instance, you don't have a smooth flat surface to work with. (And that video just shows you how to restore a surface, not remove glue from the pores of wood.)

    With water-based glues, it's more than possible to turn the clock back and get clean surfaces again.

    With epoxy it's also possible, but it will involve acetone, which will destroy surrounding finish. So it's a more involved process, but it's feasible.

    With Gorilla (or Titebond II and III), you're in trouble. They're never meant to be reversible.

    So the obvious place to start is to try the water-based glue route first. If steam and/or acetic acid won't touch it, then you go to acetone. If acetone won't touch it either, it may be time for a new neck. Or an elaborate headstock graft.
    .
    ph

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  8. #8

    Default Re: How to remove unidentified old glue

    Quote Originally Posted by Paul Hostetter View Post
    So the obvious place to start is to try the water-based glue route first. If steam and/or acetic acid won't touch it, then you go to acetone. If acetone won't touch it either, it may be time for a new neck. Or an elaborate headstock graft.
    Or.....as my father liked to say, "the difficult we do immediately, the impossible takes a little longer......"

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    Default Re: How to remove unidentified old glue

    Quote Originally Posted by Paul Hostetter View Post
    This video is barely applicable. If the headstock in question was once glued with Gorilla glue, scraping and sanding are simply out of the question. You need to clean all the glue out of the pores of the wood to be able to start over. In this instance, you don't have a smooth flat surface to work with. (And that video just shows you how to restore a surface, not remove glue from the pores of wood.)

    With water-based glues, it's more than possible to turn the clock back and get clean surfaces again.

    With epoxy it's also possible, but it will involve acetone, which will destroy surrounding finish. So it's a more involved process, but it's feasible.

    With Gorilla (or Titebond II and III), you're in trouble. They're never meant to be reversible.

    So the obvious place to start is to try the water-based glue route first. If steam and/or acetic acid won't touch it, then you go to acetone. If acetone won't touch it either, it may be time for a new neck. Or an elaborate headstock graft.
    Yes I agree which is why I suggested it would not be good news.

    The OP noted in the original post that the old glue did NOT seem to be soluble in hot water, acetic acid or acetone? So I am pessimistic I guess. I'm guessing it will require some new wood being added?
    Bernie
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  10. #10

    Default Re: How to remove unidentified old glue

    Gorilla Glue may well be the culprit. It has a more granular surface than I would expect with epoxy, but 10 minutes in boiling water left it hard as a rock. You gotta respect (and hate) such glues. I think I'll try scraping what I can, glue with tightbond, then sneak a couple dowels surreptitiously underneath the tuning gear hardware to add a bit more strength. If that fails, we'll see about a new neck...

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    Default Re: How to remove unidentified old glue

    Quote Originally Posted by NRMiller1958 View Post
    Gorilla Glue may well be the culprit. It has a more granular surface than I would expect with epoxy, but 10 minutes in boiling water left it hard as a rock. You gotta respect (and hate) such glues. I think I'll try scraping what I can, glue with tightbond, then sneak a couple dowels surreptitiously underneath the tuning gear hardware to add a bit more strength. If that fails, we'll see about a new neck...
    I have fixed a few necks (mandolins & guitars but I'm no expert. Most of the more experienced luthiers/repair guys on this forum generally do not recommend using dowels for neck repairs. The general idea is they end up making the problem worse or the neck weaker and more inclined to fail in the end. Overlays and underlays of new wood seems the method most often recommended. Perhaps some of those guys will weigh in here with advice? Best of luck.
    Bernie
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    Due to current budgetary restrictions the light at the end of the tunnel has been turned off -- sorry about the inconvenience.

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    Default Re: How to remove unidentified old glue

    This is not a recommendation, just putting it out there. I re-repaired a smashed upright bass scroll that had been glued with gorilla glue. The glue failed (surprise, surprise). It took about forty hours with scrapers, dental picks and a lot of curse words to remove the gorilla glue. I re-glued it using West System epoxy and it has held for three years now. I would not normally use epoxy on an instrument repair but I was concerned that there was enough gorilla glue left in the wood pours to stop HHG from working.

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    Café habitué Paul Hostetter's Avatar
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    Default Re: How to remove unidentified old glue

    I'm sorry I didn't catch the bit in the OP about having already tested for the other glues. If I was confronted with a failed Gorilla mess like this, I'd probably just get those surfaces as clean as I could (dental picks, whatever) so they mated well again, and do as Nevin suggested: good slow-set epoxy. And probably an understrap spanning the crack, which will restore critical strength. Gibson guitar necks have alway been badly engineered which is why this break is so common.





    Most people who do this repair spray the area so dark you can't see it.



    I rather doubt the guitar is worth 40 hours of labor, unless you don't ascribe much value your time.
    .
    ph

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  15. #14

    Default Re: How to remove unidentified old glue

    Quote Originally Posted by Paul Hostetter View Post
    I rather doubt the guitar is worth 40 hours of labor, unless you don't ascribe much value your time.
    That's what I run into in my repair business. Often the guitar is a $100-500 guitar and not worth putting more than $100 into the repair. I try to give the client options, such as, I can fix the crack, but it will still show for X amount or I can spray it to camouflage it for XX amount. With a more valuable instrument more time and effort can be justified, of course.

    Paul, your work is beautiful, by the way!

    Another thing I do is guarantee the repair, even though I know there is always a chance it may fail. I do this because I believe it instills confidence in my work in the client's eyes. I also use this as an opportunity to mention that no repair will hold if the instrument takes a fall or the owner is careless. Just an aside, I was at a pawn shop the other day and a nice lady was rearranging the guitars on the wall racks and was leaning them against amps and they were all sliding around and as we were talking I probably caught three of them to keep them from falling to the floor and finally I just ended up helping her for the sake of the guitars, even though none were of much value. She didn't realize the risk, she was just treating them like golf clubs or yard tools. I would hate to think what happens when I'm not there! (did you ever wonder how the tuners at the end of a guitar got bent???)

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