Re-gluing the back on a vintage gibson mando?

[evanelkin]

Hi folks - I'm considering purchasing a 1921 Gibson A here in town - it plays and sounds beautiful but there is a significant separation of the back from the sides. What am I looking at financially to repair this? The separation is in the vicinit of the heel and the owner assures me it has not continued to separate in the 10 years he has had it...I just don't want to get myself into a mess

thanks for your advice

feel free to post or email me directly at evanelkin@yahoo.com

[sunburst]

I can't say for sure without seeing it, of coarse, but that situation usually isn't too bad, as long as nobody has put anything in there but hide glue.
If nothing else has moved and the open joint hasn't gotten a whole lot of dirt in there, the old glue can be "reactivated", and new hot hide glue added to re-glue the seam, and it should hold.

Financially, it depends on where you take it. My guestimate would be, probably, between $50 and $100.

[Paul Hostetter]

I'm pretty sure the old glue is not reactivatable (is that a word?). Moreover I don;'t see why you wouldn't want fresh glue.

The usual situation for old Gibsons is a significant change in the outside profile of the back relative to the outside profile of the rims. Frank Ford made a jig (which you can see on Frets.com I believe) for strongarming the sides back into shape to match the back perimeter. I have tried this too and didn't have great luck: the back had simply shrunk and the amount of tension it took to force the sides in to realign everything was just scary. In addition, the neckblock is a massive piece of wood that often expands a bit while the really beefy back section there shrinks across the grain. The parting of ways is usually very serious, and the general effect is that the sides are protruding well outside the outline of the back. There's nothing in this area you can compress or force in - it's all solid wood.

So I usually get it back together as close as I can without being brutal, and rebind the back with wider ivoroid binding. If it's an unbound back, so much the better: you just need standard thickness binding to cover up the anomalies.

Does this seem to fit?

[Jim Garber]

What Paul describes is very typical of Gibson disease. My 23 snakehead A2 had it and luckily my luthier was able to remedy the situation similar to what Dr. Ford recommends. No telling whether it may happen again but so far it has been prob 5 or 6 years and it is stable.

In any case, I would have a competent luthier check it out before you purchase it, if possible. I would think it would cost a few hundred to fix.

Jim

[Paul Hostetter]

Huh? What I described was about the neckblock/heel area, which was the initial question. You can't compress the neckblock with thumbscrews. It's solid wood. Frank's rig (which I can't seem to find on his site) is inapplicable, there anyway.

[Jim Garber]

The usual situation for old Gibsons is a significant change in the outside profile of the back relative to the outside profile of the rims.

Huh, back at ya...

I think the confusion (for me at least) is the term "heel".I reread these posts a few times and -- yes, maybe it is late for me on the righthand coast -- but my experience is that the bulging out of the sides usually occurs at the base near the tailpiece, at least in the cases I have seen. If that is not the case above, please pardon my misunderstanding.

In any case, I will allow the experts to comment further on this topic.

Jim

[Paul Hostetter]

It would not hurt to hear from Evan, who posted the question in the first place!

[Paul Hostetter]

PS: Here's a little more explanation of the shrinkage and expansion issues I usually see going on.

The backs tend to shrink across the grain (red arrows pointing in)

The heel block tends to expand across the grain.
- The direction of the grain is indicated by the blue arrow
- The expansion is indicated by red arrows
- The sides bulge out most at the yellow arrows



Nothing here to compress, unfortunately.

[Antlurz]

The heel block tends to expand across the grain.
- The direction of the grain is indicated by the blue arrow

Paul....

Is it not possible that the block doesn't actually expand, but in fact only shrinks less because of it's mass than the sound/back boards, leaving the impression of expansion when comparing?

Either way, the actual inter-relationship would appear to be the same, I'd think...

Ron

[sunburst]

Here's a situation where I'd like to see a pic of the instrument originally in question. I was thinking it was a case of the neck heel and a little of the head block coming loose from the back, and pulling up slightly from string tension.
In that case, no realignment of the rim is needed, just re-gluing.
I'm not suggesting re-constituting the glue that is there and expecting it to hold. I use my steam needle that I use for neck re-sets, and "wash" out the dirt and old glue. That leaves any remaining glue in the joint re-dissolved and ready to "grab" the new glue.

As for the rim misalignment situation, I have a jig to realign those, though it's not quite like Franks. I didn't assume from the original post that that was a problem.

[Paul Hostetter]

In my experience, if the neck heel and head block coming loose from the back, and pulling up slightly from string tension, it would not be because the glue joint failed, but rather because the forces of the two glued masses changed shape as they had to and overpowered it. Which is not quite a different way of saying the glue failed, because the back and the block really changed shape. The glue joint had no choice but to fail.

In that case, no realignment of the rim is possible, and it’s not just a matter of re-gluing.

I rarely use the steam needle to wash out old glue unless it’s really dry weather and the surfaces are easily and fully exposed to that dryness. If I do, I need to count on just the glue surface drying out quickly and the moisture not getting down into the wood and remaining there to defeat later gluing and alignment of parts. I much prefer mechanically removing old glue, if there’s any in the way.

If I read the original post right, it was the big neckblock that was the problem. I agree a good photo would be helpful.

Ron – the bigger the mass, as in the neckblock, the more there is to contract or expand, depending on how that mass is able to absorb or lose moisture. Wood never expands along its grain (the blue arrow) – it only expands or contracts across it. And that expansion isn’t only parallel to the plane of the back, as those arrows show, but also from top to back, which I don’t show. In other words the block is a sponge that can change shape in two of three directions. When the block expands, which I don’t see often but I do see from time to time, the back seems to be pushed off the block. In other words, it’s thicker from top to back than when the mandolin was made, and clamping it shut is simply out of the question. You wouldn’t want to exert enough clamping pressure to compress that wood.

Ordinarily the sides remain glued to that block and even though they are inclined to shrink across grain from age, they go along for the ride because they’re thin and kind of stretch with the sides of the block. Likewise the neck itself goes along for the ride, given its grain orientation. The back however is pretty thick there, and it tends to shrink as well, so the whole seam just yields.

I know someone who has an old A with this situation. He’s been playing it for years like this (pay attention, Evan!) because the center part of the glue joint is still holding. It looks bad, and it’s probably doomed, but the neck angle hasn’t changed. I’ll see if I can borrow that instrument and take some photos. I probably need to see how it’s doing anyway. It’s always looked a bit precarious.

[evanelkin]

I just want to thank everyone for their skill and insight into the issue. I feel generally encouraged not to shy away from purchasing this instrument because of the back separation. I now need to find a luthier to repair it for me for a reasonable price...locally (NYC) or perhaps by shipping to one of you fine folks for the repair. thoughts on that?

[Paul Hostetter]

I think I'd like to see some photos.

[mando andy]

Yes -- photos would be nice -- inquiring minds want to know...

Andy

[Paul Hostetter]

If the question was asked in February, and no photos appeared during the ensuing seven months, I think the case is, as they say, closed.

[Darryl Wolfe]

No, the case is not closed completely. Paul, why does your a-model picture with the back off have a white 50's Guarantee label in what appears to be a '23 or '24 A model (based on the button shape and the ridiculously offset dovetail)

[Stephanie Reiser]

Not only the offset, but that is quite a gap behind the dovetail. But then, I have not had the back off of many vintage mandos, so perhaps that is considered the norm.
And perhaps, too, the label is for a repair. Naw, I don't think that is the case, but the font is definitely not early 20's.