what glue to use on 70yo mando w/ previous repairs?

Today I bought a "Stadium" mando for $40. as far as I can tell it's about 70 years old, and is in surprisingly good condition for its age and history.

Someone once "repaired" the separating top and back with tiny nails and an unidentified glue. There are some insignificant gaps forming now that it's been another 50 years or so, but the nails seem to be keeping things in check.

Would I be ok using wood glue to fix the gaps since the previous repairs would make taking things apart unusually difficult anyway? Or is it worth buying and learning to use hide/fish glue on it?

Titebond regular is the goto glue nowadays for instrument building/repair.

First, could you post a picture of the instrument and the repair? Not seeing either makes this guesswork a little harder. The glue to use depends on what was used to put it together in the first place, what was used for the previous repair and how clean it is right now.

Generally, glue on top of old glue has no adhesion, so squirting new glue in a seam isn’t a good idea. As Mike says, the joints have to be clean; that means old glue and dirt removed to bare wood. If the repair isn’t necessary, perhaps leave it as is, but if you want to do it right, take those tacks and glue out, read up on the subject, get some clamps and do it.
I have very little experience, but an open seam in one place may indicate other places are weak too, so beyond a local fix, it’s a good idea to tap around everywhere. An invisible crack will make a sound.

An instrument of that age would most likely have been originally assembled with hide glue. What was used for the later repair is anybody's guess.
As has been said previously, most glues do not stick very well to old glue.
An exception to this is hide glue, which sticks reasonably well to itself if the old glue has not deteriorated too much and the new glue is hot and moist enough to bond with the old glue. In the repair world, that is not a sure thing.

So, the answer in this case is to open the joint well enough to clean out as much of the old glue as possible. If the old glue appears to be something other than hide glue, I would attempt to get as close to fresh wood as was reasonably possible without compromising the shape and fit of the joint. Then, I might or might not choose Titebond Original and cross my fingers. If the old glue appears to be hide glue, I would clean it enough for a good fit and use slightly thin hide glue, heated to 140 degrees F, and cross my fingers.

Whatever I used, I would let the joint cure for at least 24 hours before removing the clamps, and another 24 hours before stringing the instrument up. Then I would watch the instrument for 3 to 7 days before releasing it. If the joint failed again, the only choice would be to open the joint completely, clean all surfaces to fresh, bare wood, re-fit the joint very well, and re-glue. In the case of a top or back, it might be necessary to open the joint an inch beyond the last repair attempt.

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Originally Posted by rcc56

An instrument of that age would most likely have been originally assembled with hide glue. What was used for the later repair is anybody's guess.
As has been said previously, most glues do not stick very well to old glue.
An exception to this is hide glue, which sticks reasonably well to itself if the old glue has not deteriorated too much and the new glue is hot and moist enough to bond with the old glue. In the repair world, that is not a sure thing.

So, the answer in this case is to open the joint well enough to clean out as much of the old glue as possible. If the old glue appears to be something other than hide glue, I would attempt to get as close to fresh wood as was reasonably possible without compromising the shape and fit of the joint. Then, I might or might not choose Titebond Original and cross my fingers. If the old glue appears to be hide glue, I would clean it enough for a good fit and use slightly thin hide glue, heated to 140 degrees F, and cross my fingers.

Whatever I used, I would let the joint cure for at least 24 hours before removing the clamps, and another 24 hours before stringing the instrument up. Then I would watch the instrument for 3 to 7 days before releasing it. If the joint failed again, the only choice would be to open the joint completely, clean all surfaces to fresh, bare wood, re-fit the joint very well, and re-glue. In the case of a top or back, it might be necessary to open the joint an inch beyond the last repair attempt.

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I'd have typed the same.

Hot hide glue is much easier than it seems. I just use a baby bottle warmer (second hand from eBay) - precise temperature isn't that important if you're not keeping the glue hot for a long period, and hot enough to get it nice and runny is what you need. Make small batches and discard, rather than making a big batch and reheating it lots of times.

Work on one section at a time. Clean out the joint as best you can, warm the wood around the joint with a hair dryer until it feels nice and warm to your hand, then brush in some hide glue and clamp. Heating the wood means your glue stays active for longer. Wipe away as much liquid glue squeeze out as you can, and you can remove the rest with a warm damp cloth once the clamps are off.

One big benefit of hide glue is that if there is a spot on the seam where you didn't clamp properly, you can just heat it up again, brush in a little moisture or glue, and then re-clamp.

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Originally Posted by ProfChris

One big benefit of hide glue is that if there is a spot on the seam where you didn't clamp properly, you can just heat it up again, brush in a little moisture or glue, and then re-clamp.

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Another benefit of hide glue is if it opens down the road it's easier the fix than with any other glue.

Hide glue.

I use hot hide glue for most everything in repairs and builds. The biggest benefit is if one has to undo a joint. I'm anticipating a heel repair on an upright. It's a 1855 with a previous repair. I just hope hide glue was used for the previous repair as steaming out a neck with other glues can be really tough. As others have said, you may have to clean the crack to bare wood, even splicing in a piece of wood for a good repair.

Here's my final thought. This might not be as old as the OP thinks it is.

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Originally Posted by MikeEdgerton

Here's my final thought. This might not be as old as the OP thinks it is.

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Or perhaps older. We still haven't seen a photo... and no information about the previous repairs. So this is speculation of practically no value.

Sorry for the lack of pictures; I have not figured out how to add them yet.

Thank you for the replies. I've decided that I'm just not experienced enough to attempt a repair on such an old instrument, and the joints are solid enough for the time being. I'll take it to a luthier if it becomes a problem.

I guessed it was 70 years old based on this:

https://reverb.com/item/13663957-swe...1940s-sunburst

They seem to be the exact same age and model, although mine has the original tuners.

How to add a picture can be found here.