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Straightforward reinforcement
A Simple Top Crack Repair
© Frank Ford, 8/8/02; Photos by FF

This old Gibson LG-2 had a pair of old cracks right near the soundhole. The cracks were about as easy to reach as any. It wasn't difficult to reach inside to add reinforcement or clamps.
Here's a view in the mirror. If you look closely, you can see that the end of the X-brace was loose from the cracks to the lining. The brace under the end of the fingerboard was loose at the end, too, but it is just out of view at the upper right corner of the picture. Undoubtedly, as the top was pushed downward, the top cracked, and the glue joints on the brace ends broke loose.
It was easy for me to reach inside and press the cracks upward, opening them so I could massage in some glue. For this repair I chose regular yellow wood glue rather than hide glue. Because the breaks were quite old and dirty, I felt more confident in getting good adhesion with a modern glue.
A quick wipe to clean off the excess.
Inside, I used my shortened palette knife to apply glue under the brace ends.
If I have glue only on the opposite surface of the knife, it follows the blade under the brace with minimal smearing of the glue on the inside of the top.
Still, there was glue to clean up with a wet towel.
My brace clamps are simple small deep throat C-clamps with cork padded jaws.
In the center, I had a flat plate of acrylic to level the cracks.
And, on the outside, a thick acrylic caul to keep the area flat and protected from the clamps

After the glue dried, I cleaned up the residue from the finish with another wet towel.

To avoid excessive flexibility in the cracked area, I added a bit of reinforcement in the form a flat spruce patch about 3/32" thick, with the grain oriented perpendicular to the top grain.
I used a single clamp to secure the patch.
Outside, the cracks are still obvious, but the top is flat and level, so the cracks don't look unstable.
And, with this reinforcement plate, the top is more rigid in the area than it had been originally.

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