Acoustic Guitar Construction

I work to keep my guitars protected from wild changes in humidity - my good friend was caught off guard this week with our unseasonably low temps and low humidity. His D-15 had been down in Salt Lake City, and the D-28 at the office.

My immediate response was to get his guitars back into their cases with multiple sponges/ziplock humidity packs to bring the moisture content back up in the wood.

His 70's D-28 has a crack starting across the bridge, and some cracks starting at the edge of the pick guard.





The D-15 looks the worst, with light showing through 4 cracks across the back.

I'm confident most of the cracks will close up - would it be good to glue with hot hide glue (per Frets.com) once they close? Just leave everything alone?

I don't intend to work on the D-28, but would be fine working on the D-15.

Any thoughts on next steps once the humidity is brought back up would be greatly appreciated.

If the cracks close up tight, I would use thin CA. Be careful to put it only in the cracks.

If there is an indent in the finish, the "filling CA" that John P used here:

viewtopic.php?f=22&t=2058

should work well. (I have used it to repair larger problems with great success.) Tape off around the fill to protect the good finish, then sand flush and buff.

You can buy it here:

http://www.gearupproducts.com/fillnfini ... ation.html

Ooooooo that is a bummer. We get HIGHER humidity down here in the winter, low in the summer. Crazy and hard to work with in a garage shop that is not insulated. Hope you can fix them up.

Fortunately these aren't my instruments, and weren't in my care when the damage occurred. Very unfortunate damage no matter how I look at it.

What do you think about using hot hide glue with the percussive application shown in this video?

https://www.youtube.com/watch?v=5i4wjJv5nkw#t=175

http://youtu.be/5i4wjJv5nkw[/youtube]

I like the idea of hide glue being more friendly for future repair, and less likely to wick into the inside of the guitar.

Daniel, hot hide glue would be perfect for this type of repair as it's almost invisible afterwards.

Just make sure you can fully close the separation with the correct humidity?

Not too sure about the 'percussive' technique though - maybe the slapping of his finger is compressing the glue in there but I would have to test this in the real world to make sure that the glue is actually filling the full crack depth and length, or maybe only spot filling - only time will tell.

I would heat the area with a heat lamp (heat gun will work too) so as the open time is greatly extended. Apply the hot hide glue along the crack from a squeezy bottle and immediately work the crack with perpendicular pressure on either side of the crack in an up and down motion. This way the glue will wick its way to the full depth of the crack (if done correctly, you will see the glue on the other side of the surface appear through the crack), you can then lightly clamp across the guitar (at right angles to the crack) until the glue has dried.
To finish the repair a few diamond shaped cleats could be added along the length of the inside of the crack.

Bob

I've used the Don Teeter method. Clearly identify the grain line, start and stop of the crack. Hydrate the guitar to close the gap -- wick in some thin CA. The magic of CA is the capillary action which will automatically seek out and fill the microscopic void. The cracks along the pick guard - BTW very common and another reason I do not like pick guards, anyway take those to reputable pro. To me those look like they'll need splinter fillers. Splinter fillers are made of the top material shaved with/from the grain. The shaving is pushed into the cracks and glued in place. This is also a Teeter method.