The Importance of a Strong Bridge Glue Joint

I play a Gibson LG-0 that my mother handed down to me—she got it as a teenager in the ’60s. It’s a great guitar and in pretty killer shape considering all it’s seen. A few months ago, I noticed that the bridge was pulling up. (I can get a piece of paper under the back of it.) I read online that you don’t have to worry about the bridge coming up on an older Gibson, because they have two bolts holding down the bridge, hidden under the pearl dots. I keep it humidified, and I don’t think it’s had much work in its lifetime. Can I just live with it as is?

—Rick, Long Island, New York

Gentle readers, we live in an exciting time, don’t we? All of the information a person could want in the world is a few keystrokes away—free, accessible, and often not thoughtfully written. Older Gibsons are great guitars and it’s no wonder that people like to obsess and chat about them endlessly, but from where I’m standing, leaving these two familiar bolts to do the whole job is a bad idea. The reasons a guitar needs a good, strong glue-joint between the bridge and the top are pretty compelling.

First, let’s talk about sound. A properly glued bridge is a solid way to transfer vibration from the strings to the soundboard—all the down-bearing pressure on those strings over the saddle will transmit vibration through the bridge and glue joint to the box of your guitar. If the bridge just sat against the top of the guitar without really being joined to it, you would lose the vibration’s energy before it had a chance to resonate the box. It bears saying that hide glue, which is crystalline in structure and very hard when dry, is a great glue to use on a bridge joint. It’s generally better than a softer glue like Titebond, which can absorb vibration. The hide glue, being harder, creates a very efficient glue joint that conducts the vibration where you want it to go.

The other reason it’s important to have a strong glue joint under a bridge is structural. Spreading the stress of the string tension over a larger area, an area the size of the bridge’s full footprint, is the safest way to do it. In fact, a bridge glue joint that has come halfway unglued can sometimes yank at the top in a scary or asymmetrical way. This can contribute to a “belly” below a bridge, and a matching dip in front of that bridge.

Let’s think about our writer’s Gibson for a moment. Those two bolts were used on most of Gibson’s flattop guitars to (they said) guide the placement of the bridge. Under the bridge plate, on each side, is a little locking washer and a 1/4-inch nut, and the bridge joint was made with hide glue. Over time, the glue has given up, leaving those bolts to do all of the work of holding the bridge down. If you haven’t started to see this yet, you may soon: Often, the top will split right in line with where the bolts are and you’ll get two cracks running from the bridge to the bottom of the guitar. That’s a pretty good reason to go for a bridge re-glue!

The basic preparation for this job is to first make sure the glue joint is released. Then we’d use heat to float the pearl dots up and out of the bridge. From there, we simply unscrew the bolts from the top and the nuts, and voila, ready for fresh glue.

Sometimes, what’s under a bridge will surprise us in the shop. Every once in a while there will be finish some of the way, or even all of the way, under a bridge. Of course, glue doesn’t really stick to finish, so we can see that the bridge was never really glued down. In this case, we carefully scrape the finish away to create a clean joint of wood-to-wood, and the sound is always much improved. We also sometimes see the mistakes made by those who were there before us. Removing a bridge can be tricky for the uninitiated, but people sometimes give it a try anyway. That’s when we get a guitar with a headache hidden under its bridge joint in the way of a big hole!

But that’s a repair for another time.

Mamie Minch is the co-owner of Brooklyn Lutherie and an active blues performer.
brooklynlutherie.com

This article originally appeared in the July 2018 issue of Acoustic Guitar magazine.