Restoration Stories - Bodies
First things first: don't panic! Cracks caused by wood shrinkage (either through age, or low humidity / central heating) are commonplace, as are loose braces.
Small cracks that close up can be glued, for longer cracks a cleat or two may be necessary to make sure everything stays together. Either way the important factor is cleanliness: clean wood surfaces will glue well, where as if the crack is full of muck then it may be necessary to clean it and/or slot it (see below) to get surfaces that will adhere to each other.
Braces come loose, either through age, or because the instrument has taken a knock on the end of the brace where it's most susceptible to breaking loose. As long as the instrument was put together with hide glue (true of almost all vintage instruments) these can be glued back together with a bit of keyhole surgery via the sound-hole. Modern instruments assembled with modern glues are harder to repair in this situation: probably the whole back would have to be removed, and then the brace removed, cleaned up, and replaced.
Now lets move on to the more interesting cases, starting with wide cracks (or those that are full of a 100 years worth of muck!). In these cases the crack is carefully turned into a fine slot, and wafer thin pieces of matching wood inserted, here's an example on a Stridente mandolin:
The observant will note that this shot was taken before I started using hide glue: which I confess is actually the "right tool for the job" in cases like this.
Once everything has been touched up you can still see the repair, but we now have an instrument that's good for the next 100 years:
In more serious cases, a mandolin like this may need it's top removing, this old mandolin by Angara and D'Isanto had complete top collapse, and with the top removed it's clearly not in a good state:
Some components had even been eaten away by those pesky wood worms:
With all new braces and the instrument back together, this one made a very nice player:
Finally, lets look at an old Gibson mandolin, also with complete top collapse:
With the back off we can see that there have been several unsuccessful attempts to fix this one before:
The solution adapted was a clean sheet: remove all the old repairs and start again, new cleats, the top cracks slotted and filled with new wood, and new braces:
Afterwards, it looks and sounds like a Gibson now: