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Thread: Trouble with Top Cracks

  1. #1

    Default Trouble with Top Cracks

    Hi. I purchased an old Army Navy mandolin a bit ago from a guitar shop in our area. It had been there forever, and the top was in 3 pieces and the back in 2 pieces. I got it home and cleaned it up. I removed the giant chunks of wood that had been attached to the top and put the 3 pieces back together with new cleats. The cracks went back together well, and we remade and replaced the braces using the Crystal Forest bracing pattern. The cracks I cleated up and all looked good. I finally got the top on last week and got it strung up yesterday. Tonight, as I picked it up to play there were 2 new cracks in the top. Not where the old cracks were. I have it unstrung now, and I am going to take the top back off. I am not sure what to do now. The wood did not seem to have any dry rot or soft areas. I am not sure what to do. I used hide glue to put the top on so I should be able to get it off pretty easily.
    Thanks for any help you might have.

  2. #2
    Moderator MikeEdgerton's Avatar
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    Default Re: Trouble with Top Cracks

    It's much easier to offer advice if you include some pictures.
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

  3. #3
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    Default Re: Trouble with Top Cracks

    Yes, we need pictures.

    I will note that when an attempt is made to force humidity into an instrument to close open cracks, there is a risk of new adjacent cracks forming. My rule of thumb is that if a crack is wide enough to pass anything thicker than a doubled up piece of printer paper through it, it should be splinted rather than trying to force it to close by pressure or extreme humidification. Another cause might be cleats that are too thick or are not sufficiently tapered on the edges.

    There may be other causes as well. Was the wood you used for re-bracing the top sufficiently cured? Was the shop humidity very high when you installed the new braces? Is there enough finish on the top to make it less susceptible to changes in humidity?

    The bottom line is that the top is under too much stress, and you will have to determine the cause of the stress to solve the problem.

  4. #4

    Default Re: Trouble with Top Cracks

    I will get some pics today when I get home. The top was actually in 3 separate pieces when I got it. Two pieces were still attached to the right and left edge and the center was just a loose 2 inch wide slice. Because of that, I wasn't sure whether or not it should be splinted. The pieces looked clean and went together well. I used thin spruce slices for the cleats. I did try to taper the edges out. The wood used for rebracing had been in our workshop for a long time and should be very dry. The humidity was about 55% when building, but has risen to about 79% this last week. There are 2 coats of stain and 5 coats of finish and then later a coat of wax.
    When I get home later today I will take some pictures. Thanks so much for the help! I was not really sure exactly what went wrong.

    I don't have a lot of experience with instruments. I have repaired antique spinning wheels for years, but I realize that this is a completely different thing, and I may be way out of my depth.
    I just have been looking at this old Gibson sitting in pieces for several years now, and thought I would take a chance on getting it playing again.

  5. #5
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    Default Re: Trouble with Top Cracks

    It sounds like you have done your homework and that you know quite a bit about woodworking. The problems may not have been caused by you.

    Something you might do is measure the thickness of the top. It sounds like the mandolin had previous repairs that were less than competent-- there's no telling what they might have done before the instrument came into your possession.

    At any rate, the top should not be too much less than 1/8" thick. If it's down around 0.100" or less, it might not hold together no matter what you do.

  6. #6

    Default Re: Trouble with Top Cracks

    Well, it is quite a learning curve, but I like to figure things out so this has been really interesting. I have measured it and it varies a lot from place to place on the top. Parts are about .120 and the thickest area is no more than .143. Is there anything you can do with a top that thins out too much?

    I have a few pictures. One includes the large pieces that were glued into the top when I bought it. They seem to have been glued down with Titebond and did remove a small amount of the wood on the top.

    The back is still pretty much OK, and the crack was pretty stable and seems fine now.

    You can see the new cracks in the picture of the top. They are not wide, but are concerning. The braces are not glued in at present, as we took everything out to start over again. The brace above the sound hole we are thinking of running all the way to the sides instead of it's original configuration.

    Thanks again for any help you might have! The braces are not glued into place, but I have notched out spaces on the base of them so they can be fitted together.


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  7. #7
    Moderator MikeEdgerton's Avatar
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    Default Re: Trouble with Top Cracks

    Over the years a whole lot of folks have re-braced these things. Unfortunately some of the threads are very old and you can't get to all the links. These threads have pictures of the original bracing as well as what others have done.

    https://www.mandolincafe.com/forum/t...Reconstruction

    https://www.mandolincafe.com/forum/t...-Navy-question

    https://www.mandolincafe.com/forum/t...navy-mandoline

    https://www.mandolincafe.com/forum/t...alrite-alright
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

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  9. #8
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    Default Re: Trouble with Top Cracks

    The top thickness sounds like it is within reason.
    I am not familiar with that bracing pattern. I took a quick look at the Crystal Forest site, and noted some differences.

    My biggest concern is that I see no reinforcement or bracing around the perimeter of the soundhole. That area is naturally weak, and your crack could have started there and spread downwards. The Crystal Forest pattern does specify a soundhole reinforcement. Even if it did not, I would want to put something there, although I might approach it somewhat differently.

    My other impression is that your cleats are larger than I would use. How thick are they?

    Also, it appears that the top was in pretty bad shape before you went to work on it. I count 5 cracks, not counting the breaks under the fingerboard and the two new ones. It is never going to be as strong as it was before the damage. I would suggest that you study some violin repair techniques to see how they approach crack reinforcement.

    If it were me, I would saw off the fingerboard at the body joint, rejoin the piece of the top under the fingerboard extension to the rest of the top and reinforce that area very well, and then re-install the top as a complete unit. When you re-assemble the instrument, I would allow at least 72 hours for the glue to cure before you string it up. Since the top has been heavily repaired, I would string it no heavier than 10-14-24-38.

    You might instead want to consider installing a new top. It might be less trouble, and it would be more reliable. In such a case, I would still remove the part of the fingerboard that sits above the body and reinstall it after the rest of the work was completed. You could finish a new top with French polished shellac with brown aniline dye, or with a brown violin maker's oil varnish and it would look reasonably in character for an Army-Navy model.

    It's also good housekeeping practice to clean up as much of the old and new glue as possible before you reassemble the instrument.

    My perspective is from a repairman's point of view. Some of the builders and other repair people might suggest other ways to approach this repair.
    I wish you luck in finding a good solution.

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  11. #9

    Default Re: Trouble with Top Cracks

    Thanks so much for all your help. I wasn't sure about removing the old and new glue. I was unsure about taking any more wood from the top. I'll do that before rebracing. The cleats are about .027 thick. I haven't made them before, and I can remake them to a better size. I'll take another look at some of the violin repair sites to get a better idea. Thanks for that suggestion. I also hadn't thought about the fingerboard, but think that is a good idea, and I will work on that tomorrow.
    I did have a reinforcement around the soundhole, as you can see by the glue. The new crack went right through it, although the soundhole reinforcement did not crack.
    I used aged spruce and it was about .025 thick as well. The top was in really bad shape. There were the 3 major cracks and then many smaller ones.
    Thanks again for all the help.

  12. #10
    Registered User sunburst's Avatar
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    Default Re: Trouble with Top Cracks

    Couple of things:
    I wouldn't cut the fingerboard off but would instead remove it in one piece. (Not easy sometimes on these old Gibsons.)
    If you get some De-Glue Goo you can remove the old and new glue without loosing any wood.

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  14. #11

    Default Re: Trouble with Top Cracks

    Thanks! I will see if I can find that stuff. That would be great! I didn't want to weaken the top any more than I needed to. I will try to remove it. I have been using a soldering iron and a palette knife slowly. The back side braces seem to be OK and solid. I have been looking at all the bracing patterns and I will try to figure out one that will work best. Hard with all the cracks everywhere.
    Thanks again
    Molly

  15. #12

    Default Re: Trouble with Top Cracks

    I know that one picture with the braces on the top looks like a mess, but I will get the old glue off and get a better bracing pattern figured out. I am going to remake the cleats as well

  16. #13
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    Default Re: Trouble with Top Cracks

    De-Glue Goo will not help removing braces. It is a jell of acetic acid, and it will dissolve glue without excess wetting of wood (unlike vinegar) but it will not seep into glue joints. Heat and palette knife (or small, limber putty knife) are standard tools for separating joints.
    http://www.de-gluegoo.com/

  17. #14
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    Default Re: Trouble with Top Cracks

    Well Lucy, the cleats are a good thickness, and the soundhole was reinforced. So far as I can tell, you haven't done anything wrong. I think that if this was on my bench and I had gotten to this point, I would be wondering if the top was beyond the point of salvage. I do believe in saving a plate whenever possible, and you can give it one more try if you want to, but this one might not hold together no matter what you do. If it doesn't, you might as well start looking for a nice piece of wood for a new top.

    If you do decide to remove the whole fingerboard, a method that works well is to buy a 1" x 5" 25 watt heat blanket from MSC or McMaster-Carr, get a router speed control from Harbor Freight to use as a temperature controller, and use your pallet knives, perhaps with a tiny bit of water if necessary. Some people use a clothes iron or a heat lamp, but I prefer the heat blanket because I can put the heat right where I want it and minimize the possibility of damaging the finish on adjoining surfaces. Whatever you use, apply heat gradually and use plenty of patience. A common beginner's mistake is to apply too much heat too quickly, which can result in scorching the work.

    Bear in mind that if you remove the whole fingerboard, you may have to re-fret it.

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  19. #15

    Default Re: Trouble with Top Cracks

    All great advice, but first I would get some perspective about what you are trying to accomplish.

    For me, I would try to save a 100 year old top before ever thinking of replacing it with "new" wood. No contest. A new top would kind of ruin it for me, certainly a last resort. Again, are you repairing/restoring or trying to rebuild/build?

    The repaired cracks wouldn't bother me as long as it holds.

    You didn't say how the neck played when it was strung up. If the neck is fine, I wouldn't think about removing the fingerboard or refretting -- first things first -- deal with the top and then see about the other things. This is a fairly big project for your first time, IMHO. An experienced repairman can work on several issues at once, knowing how one will affect the other. For a first time, I would do one step at a time. Keep it simple.

    Good luck, cool project!

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  21. #16

    Default Re: Trouble with Top Cracks

    Hi!
    I am still trying to save the top of this mandolin. I redid the braces and redid the cleats and glued it up last Saturday and Sunday. I resanded the top and rubbed it out and then put a new coat of finish on it. Then over the last 5 days I put on new top coats and rubbed them out. Tonight I have strung it back up, and we will see if it will crack again. The humidity today is about 55 percent. It has been going up and down a bit, so I will have to keep an eye on it.
    Thanks so much for all the help from everyone, and I will let you know if it cracks again. If so, I am not sure if I can save it, but I will probably keep trying. I do want to use it, and right now it sounds just as good as it did before the new braces.
    Thanks again!Click image for larger version. 

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  22. #17

    Default Re: Trouble with Top Cracks

    Oh, forgot to add that the neck is nice and straight and the frets will be OK for probably a while. The action is really pretty good, as long as the top doesn't sink ; ). I decided to leave the neck alone, and I splinted the crack alongside the neck on the left. The right side was pretty tight and I decided to leave it alone for now so there would be a little wiggle room. I keep checking the top to see if it is changing at all, but so far it is stable. I put really light strings on it, .09-.32 for now.

    Thanks again!

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