Some weeks ago I found a broken acoustic guitar down my apartment. I first thought only the headstock was broken but when I look further I discovered that half of the back was also broken.
After a complete inspection of the instrument it is, except for the back and the head, in a pretty good state and fixing it wouldn't be too hard. Anyways, even if I break it more than it was, I didn't paid for it, so it won't be a big lost :)
Last thing to keep in mind is that the guitar is not a high-end one. It is a Brighton DG-1 that costs around 70€ when new.
The back is broken in two pieces. I can take them to reuse them because there are not too injured and they still fit quite nicely in each other. The internal bracings also fit perfectly on the piece when it's glued back.
Because of the break, the gluing couldn't give back the original piece. The new one was about 1mm bigger than the hole in the body. I then keep some time adjusting the piece with a chisel and sand paper to have a (nearly) perfect fit.
I could also completly revamp the broken pieces in order to have a complelty flat joint but I was afraid that the resulting piece would have been too small for the hole. That's why I choose to just use them as they are without forcing too much.
The gluing of the headstock was really simple since the break was clean. A nice bunch of glu and clamps give it back it's youth :)
I finished the instrument by sanding the back and aroung the head joint and then applied two coats of black spray paint and spray vernish. I didn't polish to get a "mirror" effect like all the guitar because I didn't have any tool to do that.
Finally, I put a set of Light strings (.011-.052) to don't put too much strength on the head. Since I didn't have any issue for the moment I thing I'll next put a bigger gauge, mainly for sound and resonance.
To finish on this, I don't think that the new body lack any resonance capabilities. I'm not an expert and I didn't found any way to test this but even with the little spaces between the broken pieces on the back I don't think that the sound is too bad.