I found this beautiful (100 year old) mandolin in a junk store in New York City. I took it to a few vintage instrument shops to see what I could find out about it. I was told that the top of the mandolin was collapsing in and that the instrument would be virtually unplayable. Given my interest in making stringed instruments, I took the mandolin to a local luthier who suggested I try to rebuild the body and see if I could get some more years out of it. Glad I did.
Here's how you can restore that old guitar or mandolin that you find in the attic or at a local yard sale.
Step 1: Find the Problem
Notice the crease on the attached photo. The mandolin was collapsing at the point where the bridge rests along the body. After 100 years of tension caused by the strings, it was only natural that the internal structure of the mandolin would begin to deteriorate. I therefore removed the strings and the bridge to release the tension on the body. (Make sure to loosen the strings before cutting them to avoid snapping). I also took off the bridge so the mandolin could rest flatly on its top against my work surface.
Step 2: Remove the Back
Vintage instruments are generally held together by hyde glue. The best way to take them apart is with a little steam and a sharp razor. I dipped a sharp razor blade in some hot water and carefully began slicing away at the glue that fastened the back of the mandolin to its side body. (Take your time and use a bunch of razors. This took me about an hour of careful work)
Step 3: Remove the Broken Braces
Acoustic instruments are typically supported by a system of bracing. Wood strips usually span the width of the body of a given guitar/mandolin so as to prevent the instrument from collapsing under the pressure of strings. After years of use, however, bracings often break or fall off, resulting in compromised body strength. In the case of my mandolin, the bracings appear to have been poorly applied (as was often the case with mass-produced hand-made instruments). With a razor and some more hot water, I carefully removed the bracings from the top of the body, as well as from the back (which I removed in the previous step). Do your best to remove each brace in one piece as you may want to use them later.
Step 4: Cut New Bracings
I measured the width of the mandolin from various points along the inside of its body. The most important area for me to cover was the line at which the collapsing was mostly occurring as a result of the pressure of the bridge. I then found a piece of old, but solid wood and cut it to the width I measured. Notice that I did not yet shape the wood to look like other bracings (this comes later). Using wood glue, I fastened the piece inside the mandolin so it fit snugly in between the sides of the body.
Step 5: Reshape the Top
Using every sort of clamp I could find, I pressed the top of the mandolin (which was where the collapsing was occurring) onto my flat work space. The idea here to to flatten the top and reverse the collapsing of the body. Figure that since it was able to flex downwards, there is also room for it to move back into its original shape. In the case of my mandolin, I applied pressure to the bottom of the instrument (closer to the butt) first and gradually added more pressure closer to the neck over time. Be sure to clamp your instrument on multiple points of each bracing. Let the instrument sit for at least 24 hours. (I think I let mine sit for about two days)
Step 6: Finishing the Bracings
Using sand paper, a razor and a file, I shaped the bracings to make them look a bit more organic. Although they are significantly thinner than they were when initially attached as wood blocks, I left the bracings rather thick so as to ensure the strength of the instrument. This will directly impact how the instrument sounds. For me, having something that played was more important than restoring the original sound. Notice that the crease that originally plagued the top has been reversed.
After banging on various points of the top and determining that the echo and vibrations sounded suitable, I began preparing the instrument for reassembly.
Step 7: Putting It Back Together
I carefully applied wood glue to the back of the mandolin and attached it to the body. I then taped the mandolin with small pieces of masking tape (this shouldn't damage any finish) along the inter diameter of its body applying as much pressure as possible. I then clamped the back to the body and let it rest for another 24 hours. After removing the clamps and tape, I sanded the edges so as to remove all rough points, screwed the tail-piece back on and finally, added a new pair of strings.
Step 8: Play It
Sure, instruments are beautiful as static pieces of art, but really, they are meant to be played. I took this mandolin back to the luthier in NYC who originally guided me through this process and he predicted this mandolin would survive at least another 75 years before needing any more repairs. She sounds great too.