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I had just finished the lacquer curing process on my first acoustic guitar when i noticed that the lacquer had started to shrink into the center seam. During the wet sanding the shrinkage flattened out without a problem, but when set to a buffing wheel the lacquer started to separate quickly due to the heat involved during buffing. Since then i have proceeded to glue on the bridge and string up the guitar. After having string tension on the guitar and away from proper humidity for about 24 hrs. i have noticed that the spruce has started to separate slightly just below the bridge. I have now removed the strings and set it back in a humidity controlled environment and the crack has started to close. One suggestion has been to remove the neck and bridge and strip the finish and then impregnate the top with epoxy filler and then refinish. Will this hold the crack in place and allow lacquer to build up? Is there any way to repair this problem without stripping the finish? Thanks Ted

First: Do you build in a humidity controlled environment? Do you know what the relative humidity (RH) was when the braces were glued to the soundboard, and what it is now?

We have some bad news and some good news...

The bad news: Soundboard cracks and seam separations often happen because the braces are glued to the top when RH is higher than it is when it cracks. This is because the braces, which are glued across the grain of the soundboard, will restrict its free movement. So if RH where the instrument lives now is normal for this area, it is likely that you can't keep this crack closed, or a new one from developing.

The "good" news is that if the instrument is yours, and you can keep it properly humidified for the rest of its life, a repair will probably last. I usually bring the humidity up in instruments by leaving a wet sponge in a plastic tray inside the soundbox, and leaving the guitar in its case for some days (make sure nothing gets spilled inside the body). Glue the crack, and reinforce it on the inside with cross grain cleats, and hope for the best.

Epoxy on the outside is not going to help, I'm afraid.

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Rian Gitar og Mandolin