Nasty Acoustic Guitar Side Cracks

This guitar's seen better days. You can see a couple of nasty cracks along the shoulder. They begun at the preamp cutout and because of the tension on that area of bent wood, they easily spread as the centre 'relaxed' while the edges stayed in place, bound to the top and back. 

That's a nasty couple of side cracks on this acoustic guitar 

In the second image you can see that someone has had a go at repairing this damage already. The previous repairer tried using fibreglass and some mesh tape to secure things. A brace was added near the preamp cutout to reinforce it but that and the fibreglass weren't enough. The arrow shows where that brace has broken. The crack's back.

The previous repair wasn't enough to keep this guitar in one piece

Given that there's a lot of 'tension' in this tight bend, for my part, I'm planning to reinforce things a little more than the previous repair. Before I can do anything, though, I've got to remove all that fibreglass. I need to get rid of as much residue as possible to get a the best adhesion I can for my repair.

Cue the swearing. It's a fiddly and annoying job, scraping off fibreglass. 

Wood bending for guitar repair

We don't just bend wood when we're making guitars. It can be really useful for some repairs too. I've decided add a new layer of wood internally and that means bending the wood to match the side's curve in this location.

Bending wood to repair an acoustic guitar side

The patch piece before it's glued in to the side of this acoustic

Once I've got it right I cut the piece down to size. and glue it into place. This makes for a slightly intricate clamping arrangement as I want to get the crack closed and glued up at the same time.

Clamping patch in place to repair acoustic guitar side

Patch glued into place. Neater and stronger than the fibreglass. 

Here's the patch in place. It's a neater job than the fibreglass and hopefully will last longer.

Over-engineering the repair

Now, erring on the side of caution I decided to over-engineer this repair. The thing is the grain of the patch wood runs longitudinally with the guitar side. And with the crack. It's not beyond the realms of possibility that it could open again, running along the grain of the patch piece. Also, the cracks are pretty close to the kerfed lining (that secures the top and back to the sides of the guitar). This means that there isn't as much of the patch wood covering the cracks as I'd like. 

So, I added a brace too. I shaped a piece to glue over the patch piece with slight notches for the kerfed linings. The grain of this brace is at 90° to the crack and the patch piece grain. Possibly overkill but, I wanted to be as sure as I could on this one.