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One of my guitars developed a top crack. Looking at the wood, it’s along an (now) obvious fault line. Might happen on other side too. There is nothing mechanically loose under top, though I will attach spruce strips on both sides (between braces). Question is, what can I do to close the gap? CA comes to mind, but I’ve seen how CA can stain spruce yellow. Help!

Maybe paint some shellac or vinyl sealer into crack first? Then CA?

CA will not close it. Humidify and see how much you can get it to close
then reglue
if you have to fill you can use a thin sliver of wood

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

The best glue I have found for making inconspicuous repairs in spruce is high clarity hot hide glue. If the crack won't go together with gentle pressure then you may have to splint it as John said.

This time of year, the “Bag of Shame” in the corner of my shop is occupied pretty much full time with a guitar needing a crack closed. A simple guitar stand in a big garbage bag with 3 large wet sponges sitting in the bottom (so they can’t touch the instrument). You would be amazed how much cracks can close with that treatment for a week. Do whatever crack repair required, then let it stabilise for a few days in my wood room (40-44%RH) before set up.




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If the crack is really wide open though then shutting it with humidity and regluing it will just crack again down the line. If it got REAL dry and that is why it cracked then bringing it up to semi-normal RH levels say maybe even as high as 60% would work. But if takes a week at 90% RH to close it then you are forcing it and once it gets back to a dry RH it will be under great stress again. So what I am getting at is that if it doesn't close back the crack at relatively normal, maybe a bit high, RH then it will need to have a splint glued in place. CA mostly wicks into the end grain but I would still not use it for a long grain crack. TB is perfect for such a repair.