repairing crack in base of neck

[Stan Calow]

I am looking for some guidance on how to fix this crack. It is a on a Martin Sigma Classical CS-6 ('70s era) that I picked up for $20 at a garage sale. I've done minor repairs on instruments before, and don't think I need a pro on this. My first inclination is to fill with CA glue and sand it even, but maybe you-all have better idea. It is a nylon-string, so not a lot of tension on the neck. Neck is straight.
Thanks 311258

[Allan Speers]

CA glue tends to break down over time. Bad idea.

Plus, no glue is guaranteed to hold that crack forever. The best repair would be to remove the FB and dowel or screw it, but then you know that & probably know how much work that is.

If you want a fairly simple fix, I suggest glueing it first, but with something that won't break down and is not prone to creeping. (Maybe animal hide glue?) Then put a couple of long dowels (screws, if you must) from the heel, ending just before the FB. You can then put a decorative piece of contrasting wood or MOP on the heel, to hide the dowels / screws.

- I did this years ago on a fairly inexpensive acoustic gtr I had, with the exact same break, and it's held up ever since. I probably used Tightbond, which does creep and so is not the best, but I figured that using 2 screws would keep the alignment solid, which it has.
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Just realize that no pro luthier would do this. They'd remove the FB.


As for making the crackline less noticable, I have no advice. I'd love to hear ideas on this from a pro: Any kind of "semi" fix, short of completely refinishing the neck?

[roger wiegand]

It looks as though it probably extends down into the joint. If so, it's almost certainly the best solution to remove the neck and re-glue the broken joint with hot hide glue out where you can get good glue coverage in the joint and clamp it appropriately. I wouldn't expect a dowel to add much strength and I don't think screws have a role in acoustic guitar construction.:) If you do it carefully refinishing may not be necessary, though you could certainly touch it up. The problem with a "quick fix" like squirting glue into the crack is that it will make subsequent repair very difficult when it breaks again.

[Stan Calow]

Thanks Allan & Roger. Since it went so long w/o a reply I thought it was either a really dumb question or too complicated to try. I will take a better look and see if the crack goes down to the joint. Its a spare guitar not my primary, so I can afford to learn from working on it.

[Mike Sherman]

The neck really needs to come out. It looks like that break has been like that for a while and separated quite a bit from exposure/shrinkage. Even if you glued it without removing the neck, it's going to affect the FB drop-off.

[Jim Creech]

I repair a lot of that sort of thing and agree that to do a proper job the neck does need to be removed to clean the break up and get a good spread of glue. You can leave the heel in place and just remove the neck and work it that way...makes for easier alignment but just a little more difficult for sanding and finishing if you are going to take it that far.

[Stan Calow]

Thanks everyone. I see now it is more than a cosmetic fix.

[george wilson]

I'd certainly use hide glue. For one thing,it will not SHOW in the crack. Certainly DO NOT use a yellow glue! Also,hide glue dries hard and will not creep like some modern white glues.

It would be well to reinforce the heel of the neck as suggested. Personally,In see nothing wrong with a properly installed long screw,put in AFTER the crack has been closed TIGHT. You don't want sawdust getting inside the open crack before it is closed up. A screw in the heel will not affect the tone in any way.

A pearl dot or small inlay will cover the screw head,as mentioned.

I think a screw is better than a dowel,because its threads will keep the crack in compression. BUT,the screw MUST be installed correctly. Drill a hole that the screw can barely pass through down to where the crack level is. Then drill the smaller diameter hole that the threads will grip. But FIRST,be sure to drill a hole that the head of the screw will recess into. If you drill this hole after you drill the deep holes,the drill will likely not do as clean a job,if you intend to just plug the hole with a wooden plug.