Repairing a GB-27

[rstevenson]

Hello,

First, don't panic! (Just like it says on the cover of the Hitchhikers Guide to the Galaxy). It's only a minor repair, and I'm even going to ask if I should do it.

A GB-27 has come to me with a very bowed top. Very? Well, I guess it's normal for the top to bow up just behind where the string tension is pulling on it, but this hump is about 1/4" high, even without any string tension on it for the last 24 hours. So first question: is that a too big hump or just to be expected? (The ribs under the top seem solid and well-attached.)

Second, and probably related, the bridge has lifted a little -- for about 1 1/2" from the bottom end it has lifted up about 1/8" at the lower tip. I can push this back down with just finger pressure, and was thinking of putting some hot hide glue under it and clamping it down. (I have a couple of deep-throat clamps.) Good or bad idea?

Final question: what finish was used on this guitar? Shellac-based? The finish looks in pretty good condition, but the guitar could use a cleaning and I don't want to use something inappropriate.

Any and all advice gratefully received.

Rob

[charles]

Do you have any photos of the hump on the guitar top? I'm having trouble picturing it.

The bridge lifting is a rather common issue in older acoustics. You might want to contact a local luthier for their opinion on it - the original bridge is likely held by hide glue but they will certainly know more than me on the subject and can either fix it or probably give you advice to fix it yourself, and do it right the first time for a fix that will last the lifetime of the guitar.

As for the finish, I'm not quite sure - could be nitro, could be poly, could be some sort of combination of the two (anything's possible! Fender supposedly uses a combo on their thin skin nitro series) - To avoid many problems you might want to consider a non-chemical product approach to cleaning the guitar just to be safe (i.e. use a soft polishing cloth and some good ol' fashion elbow grease rather than a chemical product). There might be some tests that will tell you how to determine whether it's a nitro/laquer or poly based finish, unfortunately I don't know them off-hand.

Hope I've been of some help.

[rstevenson]

Hi Charles,

Here's some pictures. There's one with a striaght board laid across the top, with spacers under each end. The spacers are exactly 1/8" thick and the board is touching the top in the middle. Little hard to see in the pics of course. There's another extreme closeup showing the end of the bridge lifting. The rest are just for the fun of it.

(Photobucket has chopped a little off the right of each of the horizontal pics. Nice of them.)

I'm a custom furniture designer/builder with 38 years experience, including taking care of national historic furnishings for 18 of those years. So I'll be doing the glue-up, if any is required. I was asking because I'm not a guitarist, so I don't really know if the hump and the lifting bridge are issues or just cosmetics.

Rob

[charles]

That's a nice guitar!

I think the slightly arched top is intentional - my Dove copy has a very slight arch as well.

The bridge will ikely be a very easy fix for you since you have so much experience - let us know how it turns out.

[Barry]

Hi Rob, and welcome.
That is a nice guitar and apparently based on a Gibson model of some sort although I can't place it off hand. It might also be a compendium of models (El Degas is weird that way!)

I'm not sure that I agree with Charles about the "arch" being intentional, after all this is a flat top guitar
This upwards warping is normally caused by the tension pull of the strings over time as witnessed by the bridge now pulling away too. That could indicate a lack of sufficient soundboard bracing in the original construction; quite possible if they were in a "cheap" mood during that production run.

The good news
Well considering the age it's not likely to arch any more, but no guarantees.
The other good news
As you've indicated, it is a fairly straight forward procedure to re-glue the bridge as described.
The bad news
With the higher bridge position comes higher string action which can only be compensated for just so far by lowering the saddle. (You must maintain a sufficient break angle from the saddle to the pin or the string energy is lost and volume and tone suffers.) Assuming the neck is straight there's likely no relief you can get by adjusting it either. After all these years it probably does not need "adjustment" anyway.

The final (?) solution
I'm afraid the final solution to correcting high string action is a neck reset.
That means physically removing to neck and re cutting the angle at the heel to flatten the angle relative to the bridge.

So, to recap, you can easily fix the bridge but you cannot easily repair the playability, if indeed that is a problem to begin with. Best of luck. Let us know what happens.
Cheers!
Barry

[charles]

I'm not sure that I agree with Charles about the "arch" being intentional, after all this is a flat top guitar
This upwards warping is normally caused by the tension pull of the strings over time as witnessed by the bridge now pulling away too.

Could be right - if it's a bracing issue....
That's a lot of work to correct (involves disassembling the guitar and reconstructing it with new bracing).

[Barry]

Could be right - if it's a bracing issue....
That's a lot of work to correct (involves disassembling the guitar and reconstructing it with new bracing).

A neck reset could run you upwards of $500-600...but doing a sound board re-bracing is a major overhaul and rebuild and it's not likely that you'd even put that kind of effort into a Martin, unless it was an extremely rare model. And of course you'd likely bugger up the acoustic properties of the guitar if not done correctly.

Restoring an El Degas in this way would simply not make sense unless you're treating it as a project exercise for your own education. I'd leave the top alone, repair the bridge and clean 'er up. If the action is high consider using lighter gauge strings and reducing the saddle height somewhat (or removing the shims from underneath if there are any).

p.s. Those tuners do not appear to be original??

[rstevenson]

Hi again,

Turned out to be relatively easy to clamp the bridge down. Here's a few pics of the clamping. I used the small wooden block as a spacer lightly taped inside, in between the ribs so I could apply pressure at just the right spot. The ribs themselves felt tight, though they are apparently not strong enough to prevent the bowing of the top.

I did some more measuring and comparing with a straight-edge. The top is almost perfectly flat from about the sound hole centre-line up towards the neck, but has a nice oval dome shape roughly centred on the bridge.

As for the tuners not being original, I've no idea. I don't know much about the history of the guitar, or even whether it was purchased new or used. (It's not mine.)

Rob

[Barry]

Hi Rob,
Thanks for the update. Looks like the bridge, at least, is under control now.
From the picture it looks like there is some "meat" left in the saddle should you (or the owner) decide to reduce it a bit by sanding down the bottom. Again, this needs to be done carefully, and you can only remove so much before wrecking the break angle as mentioned above. You can find some good reference info on the 'net.

But before attempting that, pull it out and check if there is shim or two under it? Removing them might help correct any high string action. All in all it doesn't look too bad, and I think it'll still play reasonably well now that the bridge is stabilized.

Cheers!
Barry

[charles]

Tuners are def. not original.

Glad the bridge fix went well - the bowing of the body is probably due to the same thing that pulled up that bridge - years of string tension and failing glue bonds.

I've actually a seen some photos of people who have taken older acoustics like this, completely disassembled them, and replaced the bracing with more "modern" bracing. Seems like a ton of work... If the guitar still plays well, does not buzz like a mofo, and seems stable, I'd personally just leave it.

[rstevenson]

I don't think the owner is interested in doing any more work on it. His attachment to it is mostly personal -- his father bought it for him as his first 'real' guitar. He mostly plays electric now. I'll suggest lighter strings to him, and that he should detune the guitar a little whenever he puts it away.

Rob

[charles]

Yeah, if he's got 12's or 13's on there tuned up for 20 yrs, I could see problems arising...
Nice job on the bridge fix - your clamp system is very cool.

Thanks for sharing the guitar with us.