When cracks in the top (and bottom) approach 1 mm or more, you must fill in with a stick. Trying to press the top together to glue only works for a while, the built-in tension causes a new crack to open sooner or later. Mostly not in the glued crack, but right next to it. When filling in a crack, it is a great advantage if the stick has the same color as the top or bottom. I bought a number of replaced tops from old parlor guitars, I have also scrapped some of my own hopeless cases. With a sharp scalpel and a steel ruler, I can cut out a thin triangular stick with the old varnish left on the wide side.

One of the guitars in the batch had two wider cracks in the top to fill in. Already cut sticks were picked out. The first stick broke off, but the two pieces went well together when glued.

In order for the stick to fit in the crack, it is enlarged and smoothed out with a small metal saw and a triangular file. The stick and the crack are filed so that they almost fit against each other, then the soft spruce is pressed together rock hard between abutments with clamps when the stick is glued with hot hide glue. The glue works a bit like an oil and the stick can slide into the crack when you press on with the clamps. I use thick plexiglass as an abutment and plastic film so as not to glue the abutment to the top.

After drying overnight in a press, the stick is flush with the surface of the top and already has the right color from the old varnish. Later I will use stain to hide the repair even better. With the sticks in place, the tension in the top is reduced and the risk of new drying cracks is minimal.