Slight separation of soundboard seam
 
Hi Steve,
          I lived in Lawrence in the late 70's and I remember your instrument shop. Yesterday I found your website and I was browsing your "Ask A Luthier" section - very informative (Thank you!) and your answers are quite funny (again, Thank you!).

          I've attached pics of my little triple O, that I built about 12 years ago when was building acoustics. It's a sweet player for a finger-style guy like me. I keep the guitar on a stand in my living room, and unfortunately the dry California summers have caused the soundboard seam to begin to separate behind the bridge. It's not too bad, however you can see the finish (not the spruce) has cracked. When I put a flashlight inside the guitar, I can see light through the seam. Although the joint separated, there is no noticeable bellying on the top, and no seam failure in front of the bridge.

          Thought about cleating the seam, but that would be gluing the plate halves in their separated position. I read to 'put the guitar in the case with a humidifier to allow the plate halves to normalize to their original joint. Then work super glue into the seam. I'm concerned that this solution will leave an unsightly bead of glue on the face of the guitar.

QUESTION: What can I do to mitigate any further separation? I call upon your expertise and I thank you in advance for your input.
Best, Denny Moore

Denny,
         I don't pussy foot around with a humidifier in the case. If a seam is separated I hang the guitar over a bath tub full of hot water in a closed bathroom with a bowl of water steaming on a hot plate. I jack the humidity up to 90% and leave the guitar in there for a few hours. I then soak the crack, from the top, with Hide glue, push from inside to pump glue into the crack and put a little extra pressure across the top with a bar clamp. The lips of the crack swell with glue and as they dry the crack pulls tight. I put on a few diamond patches, spruce, matching the top spruce, about 1/2" square by 3/32" thick, with the grain running  at a 45degree angle to the crack. I use deep throated clamps, and super magnets where the clamps won't fit. The minute a crack appears people greet it by rubbing their finger across it, filling it with grey skin oils, so it is very rare to be able to make a crack disappear in spruce. You should use your case humidifier, and hopefully a whole house humidifier to keep your guitar in air no dryer than 35%. An 18" wide piece of spruce will shrink 1/8" when the humidity drops from 50% to 30%.

          Don't use superglue. It doesn't shrink as it dries, it wrecks any finish it touches, and it is oddly weak. It is very strong when the joint is fresh but, especially on hardwoods, it seems to "work loose" so the joint doesn't last long. It also has a different refractive index than lacquer, so it can make a dark spot if it soaks into the spruce. Hide glue is the best, but its ability to grip and shrink can rip chips out of your finish so be careful to get it all cleaned off before it dries. Don't be fooled by Franklyn Hide Glue, if you can't face cooking the hide granules, use Tight-Bond or Elmer's Carpenters Glue. It's great to hear from you.
 
Steve Mason

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