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Thread: Luthiers! Advice on back seam hairline crack ...

  1. #1

    Default Luthiers! Advice on back seam hairline crack ...

    Hi, I have a 2” hairline separation of the center back seam adjacent to the heel, and have seen recommendations to rub some hot hide glue into the separation. to stabilize it and stop it from lengthening (which it is definitely doing). If this makes sense to try and do, have any of the Mandolin Cafe luthiers advice on what consistency to make the glue? I was guessing thinner might be better at getting into the hairline crack. The consistency of honey? Any advice on this would be gratefully accepted! —Richard

  2. #2
    Teacher, repair person
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    Default Re: Luthiers! Advice on back seam hairline crack ...

    No thicker than honey, a bit thinner might be better. It's got to be thin enough to penetrate. You might brush the spot with hot water before you try to work the glue in.

    An advantage of hide glue is that if it doesn't take, you can touch it with hot water and make another pass.

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    Registered User sunburst's Avatar
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    Default Re: Luthiers! Advice on back seam hairline crack ...

    One of the main things is to warm the instrument. Slowly get it up to 90 degrees F or so, so that the hide glue remains liquid for as long as possible. If you are worried about drying at the elevated temperature, humidify the space where you are working.
    With the glue reasonably thin ("honey" is a bit thick for this IMO), and the work space and the work piece warm, you have nearly unlimited time to massage, rub, pat squeeze glue into the opening.

    As for wetting before gluing, I probably wouldn't. It can swell the wood and close the opening so that no glue can get in. The glue is going to wet the wood anyway. If it has been open for some time, it might be a good idea to wash the opening ahead of time and then let it dry before gluing so that the glue can be forced in.
    To wash out a crack (or open seam) I will usually place some paper towels inside the instrument and introduce distilled water to the crack from the outside using a plastic pipette. If the crack is old and dirty, it will usually repel the water and none can be gotten into the crack. Keep at it and the water will start to inter the crack. Eventually the water will immediately flow straight through the crack and into the towels inside. At that point, you have prepared the glue joint about as well as possible without taking it apart.

  4. The following members say thank you to sunburst for this post:

    amowry 

  5. #4

    Default Re: Luthiers! Advice on back seam hairline crack ...

    Dear rcc56, Sunburst, and Andrew—Many thanks for this helpful input! I will proceed as suggested. —R.

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