What can I do with a guitar with a bulging top?

[Ralph124C41]

This is sort of a companion piece to my other posting about my Alvarez RD20S that I bought online that came with a lifting bridge. I apologize for what may appear to be a double posting but I really would appreciate some advice.

Yesterday my guitar shop guy showed me the top was bulging. He placed a straight edge across it and he put in two nickels on each side to balance the beam (he could have added a dime, too). He said he thought the guitar was that way when I bought it and that is what caused the bridge to start separating, with the ends showing the most gap.

He has offered to redo the repair and hand-shape/sand the bridge to more or less follow the bulging. However, he said he couldn't guarantee the work but it would be free because it was under his warranty on his repair.

So is there anything I can do in the future to try to protect the guitar? I'm thinking switching to at least 12-gauge strings, and maybe 11s or even 10s. This will just be a bedroom guitar. The guitar I bought came with 12s, I think. I put 13s on it when I had it set up but I kept the guitar detuned to E flat to help preserve the bridge. Well, that didn't work.

So any ideas? As I said in my other post he may offer me a barter for work in his shop on my other electric guitars.

Originally Posted by Ralph124C41

...Yesterday my guitar shop guy showed me the top was bulging. He placed a straight edge across it and he put in two nickels on each side to balance the beam (he could have added a dime, too). He said he thought the guitar was that way when I bought it and that is what caused the bridge to start separating, with the ends showing the most gap.

The guitars we call "flattops" don't have flat tops. Assuming what you're describing is with a straightedge spanning the lower bout directly behind the bridge, it is well within what I'd expect on a normal, healthy guitar.

[dgt178]

....what I do with my 12 string (of which tend to be more vulnerable to "belly bulge") is use lighter strings (10's), and loosen them after EACH use....just a few turns of the tuning pegs will do it....this greatly reduces the long-term tension on the bridge and belly area.....

[merlin666]

Bulging top can also be caused by too much humidity (i.e. 70%+) - so has it been in lower humidity than that for most of the time?

[Ralph124C41]

Originally Posted by Todd Yates

The guitars we call "flattops" don't have flat tops. Assuming what you're describing is with a straightedge spanning the lower bout directly behind the bridge, it is well within what I'd expect on a normal, healthy guitar.

OK, now I'm lost. He's telling me it's bulging. Either it is or he is just trying to cover up his failed attempt to glue the bridge down. It didn't look bulging to my unknowing eyes.

Originally Posted by merlin666

Bulging top can also be caused by too much humidity (i.e. 70%+) - so has it been in lower humidity than that for most of the time?

I bought it used so I have no idea. The previous owner lived in the Northeast, like me, so much more prone to low humidity in the winter so I wouldn't think it was exposed to high humidity levels for a long period. The guitar came with a dense foam type of case. I've kept it in the case with a Planet Waves soundhole humidifier that has been properly wrung out.

And as I said I got the guitar with the lifting bridge so I am thinking it could have been caused by over humidification or the bridge glue drying out or some other reason. The seller said the guitar was in very good condition.

Originally Posted by dgt178

....what I do with my 12 string (of which tend to be more vulnerable to "belly bulge") is use lighter strings (10's), and loosen them after EACH use....just a few turns of the tuning pegs will do it....this greatly reduces the long-term tension on the bridge and belly area.....

A good idea but I'd doubt I would remember to do that. I think I would do that if I was not going to use the guitar for an extended period of time.

And for some reason I have a habit of breaking the strings when I detune and retune too much. I did that recently on my Alvarez jumbo I had just strung withe DR Rares and I broke the D and G strings for some reason when I brought the strings back to full tension. I don't know of anything I did and so maybe it was some inherent structual weakness in the strings. It was the first time I ever used DR Rares, but I have had some problems with the DR electric strings so I don't know what's happening.

Thank you for your comments. As I said I hope the guitar shop guy will make me a good barter offer on the guitar because I just don't want to have to deal with this bridge problem in the future.

[fazool]

Flat tops (as already mentioned) aren't flat - they all have a slight arch to them.

Excessive humidity (as already stated) can cause some swelling and exaggerated bulging.

Is this just bulging at the bridge?

[Ralph124C41]

Originally Posted by fazool

Flat tops (as already mentioned) aren't flat - they all have a slight arch to them.

Excessive humidity (as already stated) can cause some swelling and exaggerated bulging.

Is this just bulging at the bridge?

I don't know because I left the guitar at the shop and didn't check the back. Is there somewhere else I should check? There is no fretboard sprout.

Btw, I took the guitar to a local well-respected luthier who took a fast look at the work done on the bridge (before it started pulling up). I didn't specifically ask him to check for bulging but I'd think if it was obvious he would have said something ... but I am assuming .

[zhunter]

Originally Posted by Todd Yates

The guitars we call "flattops" don't have flat tops. Assuming what you're describing is with a straightedge spanning the lower bout directly behind the bridge, it is well within what I'd expect on a normal, healthy guitar.

Yep. Two nickels and a dime is slightly more than 3/16", slightly less than 1/4" per side. I wouldn't bat an eye at that. Bridges remain glued to tops just like that all the time.

hunter

[Diamond Dave]

Originally Posted by zhunter

Yep. Two nickels and a dime is slightly more than 3/16", slightly less than 1/4" per side. I wouldn't bat an eye at that. Bridges remain glued to tops just like that all the time.

hunter

+1 to this. Flat tops aren't flat but are called that because they aren't arch tops. 1/4" on either side of a straight edge placed behind the bridge is what I've read is well within the normal radius of a flat top, and wood glue should easily hold a bridge down with that small amount of radius.

[tippy5]

I Bought a CS guitar with Englemann sanded to .105" spec. It sank in front of the bridge twice. Once after warranty. It was a sweet claro walnut warm tone that sounded like a high end nylon string with treble sparkle. I have recordings of it before its demise.

I asked them about the top being too thin, or not stiff enough. That was a lesson for me, and I presume for them too, that top's need to withstand light string tension. Not to mention additional medium string set tension. I don't know enough about the 1/4" to 5/16" bracing to comment but maybe that's why?

Or the top radius. My Gibson has a round top I think 25"? You want to ask your luthier what he measures the domed top radius - Across the whole lower bout. Then maybe ask to see where any deformation is under the straight edge.

[Ralph124C41]

Originally Posted by zhunter

Yep. Two nickels and a dime is slightly more than 3/16", slightly less than 1/4" per side. I wouldn't bat an eye at that. Bridges remain glued to tops just like that all the time.

hunter

Exactly right. Two nickels and a dime equals 5.25mm in thickness, according to the U.S. Mint specs, which equal only about. .207 inches so well under .25 inch. And it's closer to 3/16 inch (.188 inch). Of course I am guessing at the dime-sized gap. Even if it was three nickels (which it wasn't) that would be 5.85 mm so still about .23 inch.

(I like numbers. I was a math major until my third year in college. Then I switched to English and later to journalism. Go figure.)

I don't know what is wrong and I don't think the guy knows either. I still think he just did a poor job with the repair, or the glue was faulty, or he didn't let it age long enough. I'm certainly no expert but I think the bridge should not come up again in a couple weeks just with strings at this reduced tension.

[MartyGraw]

I have an 1973 Epiphone that I picked up for $65. It is actually in pretty good condition with the exception of the total junk tuning machines and it had a very excessive belly bulge that was stating to lift bottom side of the bridge. I put some wood glue in a syringe and squirted it into gap on bridge then I installed a JDL Bridge Doctor. There are pro's and con's on this little thing, but I am in the pro column. It worked great. Settled down the top and lowered the action. I had some old gold Grovers hanging around. Took out the adjustable saddle and got a blank piece of bone to carve a new saddle. For less than $100 I have a great little campfire guitar. It sounds surprisingly good and plays fantastic..

[JeremiahB.]

Sounds like you need to find a new guitar tech that actually knows the physics of an acoustic guitar. As Todd stated, virtually all flat tops are built with a radiused top, whether it be a 25' radius, 40' radius, etc. and a straight edge spanned across the lower bout of the guitar, would not lie flat at all. On top of that, it's also completely normal for a guitar (I should say "good sounding" guitar) to have a "belly" behind the bridge due to the excessive pull of the strings vs. the light bracing. In the words of Normal Blake, "Never trust a guitar that doesn't have a belly." While heavier bracing that is shifted further away from the sound hole may reduce the propensity to belly behind the bridge and may structurally be more sound, it also guarantees you will never want to play the **** thing because it sounds dead and lifeless.

I had a buyer return a guitar to me for exactly this reason. Even though, I and his own luthier/tech explained it's normal to have a slight belly behind the bridge, he was adamant that I had tried to rip him off and that the internal braces were failing even after numerous photos were taken of the internal bracing showing there was no failure whatsoever. So I refunded his money, got the guitar back, and still own and play it to this day. I sure am glad he returned it - it's one of my favorites.

Maybe the fault lies in his technique of re-gluing the bridge. I would hope that he sanded the bottom of the bridge to correctly match the curvature of the top in the exact area that the bridge will be glued. The easiest way to accomplish this is by taping some sandpaper to the top of the guitar where the bridge is to be glued, make several pencil marks across the entire bottom of the bridge and sand until there are no pencil marks left. Then dry fit to make sure there are no gaps and you have a perfect joint and glue.

[JeremiahB.]

Ok - I just re-read your first post and found this part interesting:

"He has offered to redo the repair and hand-shape/sand the bridge to more or less follow the bulging"

If he didn't do this the first time around, it's no wonder the bridge re-lifted. As stated in my previous post, the curvature on the bottom of the bridge must match the curvature of the top in the area at which it will be glued. This is easily accomplished by using the technique outlined in my previous post. I would hope that he would re-do it for free, especially if he didn't do it right the first time. The amount of curvature your outlining should not cause a bridge to lift. An ill fitting joint between the bottom of the bridge and top of the guitar would cause it to lift, which without personally seeing the guitar, would be my best guess.

[Steve DeRosa]

I'd defer to an expert opinion:

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