Today I received a Cello from Shreveport Louisiana, it had a crack on the top of cello, while removing the top we realized, a portion of the cello top was just hanging on by a few fibers and as we moved it those fibers broke and we had 2 separate pieces, Below is the repair process start to finish.
Clamping the crack
I did not take any picture’s of our clamping method (Trade Secrets).The hardest part of these kind of repairs is figuring out a way to clamp the broken piece back to its original position…sometimes you can use certain clamps, sometimes you have to makes a special clamp just for this repair, luckily for this one I was able to use a few of the clamps we have in the shop, after you get it clamps together and know it will work, the you have to take it all apart again and then glue it and put it all back together again. On this cello I had to glue it twice to get the proper alignment, first time I glued half and let it dry over night, Second time I glued the other half and let it dry over night.
The Tools Used
Various clamps used in this repair, the two pieces fir together fairly easily once we got the correct way to clamp them figured out, we used 3 of the long brass clamps you see to hold the 2 pieces together and also to put pressure on them as well. the black clamps are used in combination with a thin strip of Plexi glass to keep the two pieces level and to insure a tight glue joint. The smaller brass clamp you see is to bring the two pieces together at the bottom end and apply pressure there to keep the alignment right. And the other clamps we used are for gluing the top back onto the cello.
After 2 days of the glue drying we took all the clamps off and cleaned up and excess glue, then we applied 2 different kinds of reinforcement’s. The first we used are called “cleats” they are a small piece of spruce flattened so it fits perfectly to the cello top and shaped, so as to be not to thick and not to thin, they are installed so the grain of the cleats crosses the crack to add extra strength to the glue joint, the crack on this cello as well as the grain are going in a vertical direction so we installed the cleats with the grain going in a horizontal direction and clamped them in position. After the cleats we added cloth in between each cleat to further reinforce the cello, this is a crochet cloth soaked in hot hide glue and applied along the crack and glue joint, this method of applying glue soaked cloth was even used by Stradivari 300+ years ago. after you apply the cloth and clean up any excess glue let the whole thing dry for about 2 or 3 hours before gluing the top back on.
Gluing the Top
After heating the glue, and getting it the right consistency, we apply a thing layer of the hot animal hide glue all along the Cello lining and blocks, we start at the bottom of the cello just before the end block (We glue end blocks last) and work out way up to the top, putting a little extra glue on the corner blocks, and making sure not to let the glue drip down the sides, if it drips down the side we clean with hot water before continuing, when all the sides have glue we apply glue to the bottom and top end blocks and place the top onto the cello, Align the top and clamp the cello starting with 1 clamp on center of the saddle to keep the alignment and then 1 on each side of the neck making sure there is no seem under the finger board where the cello top meets the neck, then clamp the corner blocks and then the rest of the body checking the alignment as you go. After its all clamped clean up any excess glue with hot water and a soft brush then let it all dry over night.
Touching Up The Crack
Because the cello cracked if leave a break in the varnish that you can see and feel, I applied a special pore filler we use all along the crack and let it dry, then I used a scraper to scrape off any excess without damaging the original varnish, Sanded it so no marks could be seen and applied thin coat of Shellac and used special cloth sand paper and oil to sand it smooth and polish it to match.
Then we put it all back together unless you look closely it is vary hard to see the crack and with the reinforcements applied to the inside there should be no other future problems with the crack.
There are many methods and techniques for repairing this kind of damage, on less expensive instruments we can do this repair without removing the top and still installing cleats. This is the method I chose because it is quick clean and efficient and everything fit back together fairly easy, if they did not fit then I would have to figure a different technique luckily it all worked out and looks perfect.