The second mandolin on my repair bench proved to be a bit more challenging. At first, the owner and I thought it would take little more than reattaching the fret board, repairing some binding, repairing some non-structural surface cracking, a thorough cleaning and putting on a new set of strings. It turned out this old mandolin had been worked on before and was in need of additional top and brace repairs. According to the owner, this instrument spent a lot of time over the past few years in extremely dry conditions. So, I was not terribly surprised when I found the top beginning to cave in under the tension of a new set of strings. The last few times I've had a chance to work on this mandolin have been dreary, rainy days. Considering how dry this mandolin had been, all the moisture in the air could only have helped.
The case of this mandolin has both historic and sentimental value. Note the Delta Airlines unchecked baggage tag.
The fretboard was detached when I first inspected this instrument. The binding for the most part was in great shape, and the dovetail joint was still holding together well.
The intricate binding was split at one of the seams but was intact. With a little minor probing, I started finding out how brittle and fragile the wood and binding were at this corner. A little taping after some CA and acetone were all it would take to fix her up there.
After removing the few remaining strings and her tailpiece cover plate, I started thinking about the order in which I would make the repairs.
I used some steam to clean off the old glue and make sure there weren't any hidden cracks in the fretboard.
After removal of the pickguard, I found evidence of an old repair. Despite the top showing signs of distress, there was a repair cleat behind the crack that made things appear to be structurally sound.
After clamping and cleaning up the excess glue, I brought the repaired mandolin indoors and kept her in there for a few days while the hide glue dried.
Satisfied with the reattachment of the fretboard, I removed the clamps and moved on to repairing the surface cracks with yellow carpenters glue.
Some scraping and sanding with a small file, sand paper and steel wool took care of most of the remaining squeeze-out glue and final cleanup of the seam between her fretboard and neck.
A small amount of the fretboard binding had come loose in the process. I used a little CA to make the repairs to it, as I eventually did with the top panel body binding repair she needed. While the CA dried, I removed her tuners and began cleaning and polishing all of her exterior surfaces.
As I prepared to put the strings on, I noticed some separation at the back panel. After applying some hide glue, I applied some painters tape to hold things in place, and moved on to stringing up this mandolin.
As I applied tension to the strings, the condition of the top became apparent. Clearly, some additional repair work was required. I contacted the owner with the bad news, and we agreed it made sense to make the structural repairs at this time. Determining the full extents of necessary repairs and making them through the sound hole would not have been possible. So, the next step was removing the back of this mandolin from her sides.
Starting at the corner of the back I had just repaired, I used a combination of sharp tools and heat to release the glue bond between the back and sides. Fortunately, her back came off easily with minor collateral damage, and two of the back braces remained attached to the sides. These two braces were enough to provide the required stabilizing force to keep the sides from warping while I assessed and made repairs to the top panel.
The middle back brace was barely attached to the back panel. I used yellow carpenters glue for repairing this collateral damage.
With a little closeup inspection, I determined the root cause of the top panel failure was inadequate bracing. Unlike the other braces in this mandolin, this one did not extend between the sides and top panel. Although some instrument builders purposely leave the braces short to allow the top and bottom plates to vibrate, that clearly was not the design intent with the rest of the braces in this instrument, so I doubt it was the intent with this one. More likely, it seems to me this short brace was the result of design or construction error or oversight.
To keep as true as possible to the original design, I decided to replace the brace. In order to do that, I first had to remove the existing brace.
With full string tension, the fretboard had been pushing on the top and contributing to the forces that led to the failure. Without string tension, the fretboard was pulling the top panel outward. Neither condition is desireable without proper bracing, and realizing this was the situation also meant a neck reset was not out of the question at this time. So, before removing the brace, I released the fretboard from the body, so it could be properly attached while making the bracing repair.
With the fretboard released from the body, I used a hot and sharpened putty knife blade to remove the the old brace along with the cleat from the previous top panel repair.
To help restore the intended convex shape to the body, I made the replacement brace with some camber.
To accommodate the longer brace, I cut into the generous side material just enough to form the two gaps needed to receive the brace ends between the top panel and sides.