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Thread: Guitar repair -- fixing a big split in the sides

  1. #1
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    Default Guitar repair -- fixing a big split in the sides

    I haven't been in my shop all fall, because of allergies and a writing assignment. Yesterday, I took a big hit on the inhaler and went downstairs to start clearing stuff off my bench.

    A few months ago, a friend in Toronto gave me this to fix:



    That cartoon anthology is in for repairs, too.

    The split ran around both mahogany sides, and went straight through the heel. Fortunately, the sides had not lost their shape & when you pressed the two halves together things lined up pretty well:


  2. #2
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    Default Re: Guitar repair -- fixing a big split in the sides

    Was it a mysterious flaw in the wood or did the guitar take a fall?
    Goat Island Skiff and Simmons Sea Skiff construction photos here:

    http://s176.photobucket.com/albums/w...esMan/?start=0

    and here:

    http://www.flickr.com/photos/37973275@N03/

    "All kings are not the same."

  3. #3
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    Default Re: Guitar repair -- fixing a big split in the sides

    The value of the instrument is largely sentimental. My friend is Brazilian, and this is the guitar on which he learned samba and bossa nova, as a kid.

    It's Mexican, from the guitar-building town of Paracho:



    It was made quickly and cheaply, but there's no "fakery" in this guitar. The top and back woods are solid, the rosette is real, and it has had hard use:



    The lacquer finish is chipped and crazed, but these are marks of ordinary use and I won't try to replace the old finish. Even a modest instrument should be repaired respectfully, and the standard, these days, is to change as little as possible, record what was done, and ensure that any alterations can be easily reversed.


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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by MiddleAgesMan View Post
    Was it a mysterious flaw in the wood or did the guitar take a fall?
    I think it took a hit, some years ago. Since the crack runs right through the heel, it must have been a sharp blow.

  5. #5
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    Default Re: Guitar repair -- fixing a big split in the sides

    The construction is traditional, but the glue isn't. Looking down through the soundhole, you can see a big blob of squeeze-out around the Spanish heel. It's probably some kind of PVA adhesive.



    The heel is rough -- just sawn, with no carving or sanding -- but intelligently shaped.
    Last edited by Bruce Taylor; 02-16-2011 at 08:08 PM.

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    Default Re: Guitar repair -- fixing a big split in the sides

    It will be interesting to follow your repair technique. I wouldn't know where to start....

    What is the first step, remove the back?
    Goat Island Skiff and Simmons Sea Skiff construction photos here:

    http://s176.photobucket.com/albums/w...esMan/?start=0

    and here:

    http://www.flickr.com/photos/37973275@N03/

    "All kings are not the same."

  7. #7
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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by MiddleAgesMan View Post
    What is the first step, remove the back?
    Nothing so drastic. Unlike fiddles, guitars are not built to be disassembled, and removing the top or back is a major operation. It's only worth doing on a fairly valuable or historically interesting instrument.

  8. #8
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    Default Re: Guitar repair -- fixing a big split in the sides

    Hot hide glue is best, for most restoration. It is strong, reversible, and won't interfere with future repairs. However, it has a very short open time and this was a long crack. The crack in the heel would have to withstand string tension, and I wasn't confident that I could get all the parts lined up and clamped before the glue started to cool. It would be difficult to do in sections (when one part of the crack was closed, all parts were), and I preferred not to add a spline or dowel to the heel. So, I decided to use yellow glue on the crack itself.

    Closing it was easy enough, since the sides were not distorted and the break was quite clean. I don't have many pics of this step, but there's not much too it. I used a small paintbrush to slip a line of glue into the crack, and closed it up with masking tape. It's pretty much the same technique that I use for applying bindings & purflings on a new guitar.



    I used just one clamp, at the heel.


    As long as I've got the glue out...

    Last edited by Bruce Taylor; 11-07-2010 at 09:24 AM.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Bruce Taylor;2768434

    So, I decided to use yellow glue on the crack itself.

    Closing it was easy enough, since the sides were not distorted and the break was quite clean.

    [IMG
    http://i282.photobucket.com/albums/kk273/BruceDSTaylor/Guitar%20Repair/crackcloseup.jpg?t=1289141122[/IMG]

    I used just one clamp, at the heel.
    Oh the horror!! Stand by to receive shot lines fore and aft , the boarding parties will be here soon!!!


    Looks good , prolly get another 30 years out of it! Nice job!

  10. #10
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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Paul Girouard View Post
    Nice job!
    I'm not done.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Bruce Taylor View Post

    I'm not done.
    One step at a time , it will be done. Yes, I'm projecting some what. Rome wasn't built in a day , although I think many people today expect instant results.

  12. #12
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    Default Re: Guitar repair -- fixing a big split in the sides

    I won't attempt an absolutely invisible repair. Big chunks of lacquer have come loose around the crack, and the remaining lacquer is in poor condition. A truly invisible repair would require levelling the old finish and rebuilding it over the entire side.

    A fair bit of bare wood is showing, though, and it should be made less conspicuous. I use razors to scrape the finish level around the crack, and wipe a good layer of blond shellac over the areas that need touching up. I'll do it by repainting grain lines and matching the colour of the newly exposed wood to the seasoned mahogany around it. Since the paint sits over a layer of shellac, it can be stripped away at any time with light scraping and a bit of alcohol.

    I'll apply acrylic paint in glazes...earth pigments, mostly: raw umber, burnt sienna & yellow ochre:



    The paint dries pretty quickly, and glazes can be built up in layers.



    Grain lines need to be darkened:


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    Default Re: Guitar repair -- fixing a big split in the sides

    Bruce, I'm very impressed with your finish touch-up. When you say "acrylic paint," is your base clear acrylic lacquer, or something else? (I've used nitrocellulose lacquer mixed with pigments for similar uses, but yours is lovely.)

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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Horace View Post
    Bruce, I'm very impressed with your finish touch-up. When you say "acrylic paint," is your base clear acrylic lacquer, or something else? (I've used nitrocellulose lacquer mixed with pigments for similar uses, but yours is lovely.)
    The existing finish is nitro, or something similar, but I've applied a thin layer of shellac over that and over the patches of bare wood in the chips and divots (some of these patches were a couple of inches wide). The paint goes on in transparent glazes, over the shellac. Sometimes, I'll add another a layer of shellac and paint over that. The goal is not stability & permanence -- though I don't think that will be a problem -- but reversibility.

    Oil pigments are nicer to work with, but much slower. This will be ready to take a polish on the same afternoon.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Next, I have to reinforce the interior of the guitar by reinforcing the area around cracks. This reinforcement can be made from strips of linen soaked in hot hide glue. However, I'll use thin spruce braces, made from a scrap of old soundboard wood.



    I'll use rare earth magnets to clamp these in place. The magnets also provide little handles for manipulating the strips.


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    Default Re: Guitar repair -- fixing a big split in the sides

    I melt down some glue, brush it on the brace, and reach in through the soundhole to tack it in position. Then, I apply a couple more rare earth magnets to the outside, and let it cure:






    I put them at 2"-3" intervals all around the crack.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Hey! Does Lee Valley know about this use for rare earth magnets?

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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by katey View Post
    Hey! Does Lee Valley know about this use for rare earth magnets?
    Probably...they're used a lot in repair lutherie, these days. They're pretty handy for hanging school lunch schedules on the fridge, too.

  19. #19
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    Default Re: Guitar repair -- fixing a big split in the sides

    It needs a new heelcap:



    Clean up the heel with chisels and a file:



    I keep small scraps of hardwood for this kind of job.



    Macassar ebony, no veneer:


  20. #20
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    Default Re: Guitar repair -- fixing a big split in the sides

    My word, thank you for starting this thread! Are you a professional luthier?

    Another question, from an amateur's point of view: why did you opt for yellow glue for an edge repair of a solid piece, rather than epoxy? Lute ribs constructed with epoxy and nylon cloth seam strips appear to be bullet-proof, and since one is not apt to disassemble a repair of the bouts and heel of a guitar, I thought epoxy would be less prone to movement or release due to string tension under similar conditions?

  21. #21
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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Horace View Post
    Are you a professional luthier?
    Nope...it's just a hobby. I've posted quite a few guitar-building threads here, over the years (probably before your time ).

    Another question, from an amateur's point of view: why did you opt for yellow glue for an edge repair of a solid piece, rather than epoxy? Lute ribs constructed with epoxy and nylon cloth seam strips appear to be bullet-proof, and since one is not apt to disassemble a repair of the bouts and heel of a guitar, I thought epoxy would be less prone to movement or release due to string tension under similar conditions?
    Epoxy would work fine, but in this situation it doesn't offer much improvement over a Titebond-style AR glue (not enough to justify the cleanup issues, at least). This is a tight, clean joint, so gap-filling (epoxy's forte) isn't an issue. The strength of AR is more than adequate, here, I think.

    Also, in my experience, epoxy is just as likely to creep under load as AR glue. I've experimented with using West System to glue guitar bridges, and haven't been impressed at all. I've seen AR creep under load as well (but I don't think it will, in this guitar's heel). These days, I only use hide glue for bridges. So far, so good. And I still use epoxy for pore-filling on new instruments.

    I haven't heard of using epoxy-soaked cloth in lutes...sounds interesting.

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    Default Re: Guitar repair -- fixing a big split in the sides

    My hat's off to you if you can get reliable results with (traditional) hide glue, but I've never persisted to the point of reproducibility. Epoxy just seemed like a good idea when I started, and I haven't advanced to the point of observing traditional techniques.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Bruce Taylor View Post
    I haven't heard of using epoxy-soaked cloth in lutes...sounds interesting.
    Oops. I meant ribs assembled with epoxy, not an Ovation-style body.

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    Default Re: Guitar repair -- fixing a big split in the sides

    For your edification, Horace, and for any others that may have missed them:

    http://forum.woodenboat.com/showthre...ign&highlight=

    This was great, thanks Bruce/
    Steve Martinsen

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    Default Re: Guitar repair -- fixing a big split in the sides

    Thanks for the link.

    This might be a good time to gather links to earlier threads on this topic into one place. I found this one: Building a Guitar 1 -- The Rosette. Are there any others?

  26. #26
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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Horace View Post
    Are there any others?
    I did eight threads on building a classical guitar:

    The Rosette

    Some Thoughts on Design

    Moulds and workboard

    The Neck

    Top and Back Plates

    Bracing the Top and Assembly

    Binding, Fingerboard and Bridge

    Finish and Setup



    I did another series on steel-string construction, but that was less detailed.
    Last edited by Bruce Taylor; 11-08-2010 at 03:17 PM. Reason: Links were broken

  27. #27
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    Default Re: Guitar repair -- fixing a big split in the sides

    I put a very light French polish on the sides, then strung it up.

    The action is acceptable (probably about where it was the day the guitar split in two). It doesn't sound too bad...a bit dull in the midrange.

    It's not "as good as new," but it's better than before.



    From the scratches on that top, I'd say my friend Ricardo has a distinctive playing style.

  28. #28
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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by Horace View Post
    Oops. I meant ribs assembled with epoxy, not an Ovation-style body.
    That's what I was picturing...cloth along the seams, where a traditional lute-maker would have used parchment, right?

    For me, hide glue didn't become predictable & easy to use until I quite messing around with double boilers and candy thermometers and bought an electric glue pot.

  29. #29
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    Default Re: Guitar repair -- fixing a big split in the sides

    I can't even see the repair, what a collection of talent on this forum. I like it.

    Did you know that the strongest hide glue you can make is Knox gelatin and water? Heat the water to just short of boiling, add enough gelatin to bring it to the consistency of maple syrup, let it sit for a while and use it. My son was making authentic traditional bows, sinew and hide glue backed, and we learned everything we could, including making our own from deer hides, a long smelly process. Then we read about some extensive experiments done by a prominent bowyer and learned about the gelatin. It seems that it is the purest form of colagen available. He tested it against epoxy and found that it was at least as strong.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Bruce, thanks for the links. A very impressive repair--I'm inspired to de-clutter the workshop and try to finish up some projects this winter.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Quote Originally Posted by gibetheridge View Post
    Did you know that the strongest hide glue you can make is Knox gelatin and water? Heat the water to just short of boiling, add enough gelatin to bring it to the consistency of maple syrup, let it sit for a while and use it. My son was making authentic traditional bows, sinew and hide glue backed, and we learned everything we could, including making our own from deer hides, a long smelly process. Then we read about some extensive experiments done by a prominent bowyer and learned about the gelatin. It seems that it is the purest form of colagen available. He tested it against epoxy and found that it was at least as strong.
    That's very interesting, and news to me. I'm going to try it out.

  32. #32
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    Default Re: Guitar repair -- fixing a big split in the sides

    I see Frank Ford has done an article on using Knox gelatin: http://www.frets.com/fretspages/luth...tchenglue.html

    350 grams is very strong (the Behlen's I use has a gram strength around 250, IIRC) and will have a correspondingly short open time. As Ford points out, it's not a cheap way to buy your glue, though.

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    Default Re: Guitar repair -- fixing a big split in the sides

    Very informative and very fun to watch Bruce. Thank you for taking the time to share your hobby with us.

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    Default Re: Guitar repair -- fixing a big split in the sides

    As ever, Bruce, it's a real joy to see your work. Thanks.
    "The true mystery of the world is the visible, not the invisible." - Oscar Wilde

  35. #35
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    Default Re: Guitar repair -- fixing a big split in the sides

    I just noticed that the links I posted above were all broken (because of the last vbulletin upgrade, I guess).

    Here they are again:

    The Rosette

    Some Thoughts on Design

    Moulds and workboard

    The Neck

    Top and Back Plates

    Bracing the Top and Assembly

    Binding, Fingerboard and Bridge

    Finish and Setup

    I went back and changed the links within those threads, too.

  36. #36
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    Default Re: Guitar repair -- fixing a big split in the sides

    Nice to see you back in the shop.
    Did the histamines behave?
    R
    "Now Ron,don't you do anything stupid!" - Grandma B.

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