Today we fixed up a Martin guitar that had several cracks in the top. To do this, we make a cleat and glue it over the crack. Sounds simple, right? The devil is in the details…
First, we make a cleat out of matching wood to go over the crack. Here, Spencer has made a perfectly symmetrical hexagonal cleat out spruce:
Next, we make a sandwich out of the cleat, some wax paper, and powerful rare earth magnets. We mark the magnet to point in the direction of the wood grain of the cleat, which will help us place the cleat in it’s proper position across the grain on the guitar’s top.
Next we apply a dab of hide glue to the back of the cleat:
Then we place the cleat across the grain (taking note of our arrow we marked on the magnet) inside the guitar – placing the cleat across the grain on the top makes the joint much stronger:
Then we put another powerful magnet on the top of the guitar, which holds the cleat in place:
The hide glue takes about 24 hours to dry completely – once dried, the cracked top is stronger than ever before.