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A very subtle, almost invisible, itsy-bitsy, teeny-weeny, tiny little crack has appeared in the varnish finish where the center seam runs along the top of one of the guitars I've built. You really have to get right down close and angle the guitar in the light just so to see it, but it's there. This is a spruce top that was joined with Titebond and I worry that me trying to "fix" things may result in an ugly mess and leave the guitar in worse shape than when I started. I haven't had to address this before and am wondering what you folks might recommend.

Thoughts?

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George :-)

A little diamond shaped cleat or two on the inside will stabilize things. I have often wondered why we put a reinforcing strip on the back but not the top, so starting with my most recent instrument I have put a couple of these on when it ws easy to do, before I closed the box

Ed

Good idea, Ed. I've started doing that as well but this particular guitar does not have any cleats.

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George :-)

George my friend step one for me would be to determine if this is indeed a crack that goes all the way though and not just a crack in the finish and/or a sunken glue line in the center seam.

Here's my approach:

1) Naphtha dripped onto the crack top side while with inspection mirror and light checking inside for a wet spot. If the wetness shows up on the inside you have a crack in the guitar center seam. If not it's a finish crack or sunken glue line. Naphtha will not harm any finish and will dry away in minutes.

2) If one above is positive for a crack (see the flow charting here...) carefully inspect the crack manipulating it with clean hands (finger dirt loves guitar cracks and colors them dark forever more so I always wash my hands first) to see if it is all the way closed.

3) If it is not closed bag the guitar in a quality garbage bag hanging it from the headstock for a couple of days with a large car wash type sponge and about 8 ounces of water in the bag. This will swell the crack shut.

4) Once the crack is closed a couple of days later and out of the bag and with clean hands ready you will need the following:

1) The Titebond that you originally used
2) Some waxed paper
3) rare earth magnets or long reach clamps that can through the sound hole reach the entire length of the crack
4) something flat but slightly flexible to use as a caul and I like plexiglass for this with the edges sanded so there is no scratching.

5) This is a method that I have been developing for a couple of years now and what's different about it is that a closed crack is difficult to get thick glue into. So I water down Titebond 50/50 and while manipulating the crack with those clean fingers let it wick into the crack until I see beads of glue on the inside of the box. Next I squirt on some full strength Titebond and pump and manipulate the crack again with my fingers trying to push as much full strength Titebond into the crack as I can get.

The thinned Titebond serves to size the joint AND help the thick stuff wick in as well and it works very well for me.

6) When you have glue in there and can see the glue going all the way though on the inside wax paper down first, ensure the crack is level, then magnets or clamps.

7) Clean up dried glue off top the next day with warm water on a Bounty paper towel (Bounty won't scratch the finish, others will....).

It's possible to have the fix invisible as well.

Now once the crack is closed, glued and has dried over night is when you go back inside the guitar and be sure that the tone bars spanning the center seam are also still glued in place under the crack. Often they are not. If not using something very thin such as a .0015" inch feeler gage push more glue under the loose braces and clamp again with the flat caul on the topside and let dry.

Lastly you install cleats with the grain running across the top grain. Cleat size can be very small or larger and I make mine a little over 1/2" long and less than this wide. The cleats are glued in place on the inside usually equal distant between the tone bars for maximum strength.

There are lots of ways to fix a top crack and this is just one of them. I've used this method commercially hundreds of times with great success and no returns or cracks reopening up.

Additionally the braces and the top crack can have these two steps combined if you think it out and do dry runs to be sure you have all that you need when it's important and the glue has been deployed.

Ideally we would love to be gluing a crack where the old Titebond has been cleaned out but doing so here will likely show and possibly damage the crack further degrading the cosmetics of the repair. With HHG the old glue can be reactivated but not so much with Titebond but Titebond will stick to itself and always has for me.

Hope this helps and if you have any questions feel free to PM me or call me at work tomorrow and I will be happy to walk you though it. My work number is on my web site for Ann Arbor Guitars.

Hesh,

As always, a very concise and clear explanation. I'd call it a "virtual toot". I am salting your explanation away for future reference. It's great to have a buddy in the guitar-repair/restoration business.

BTW, any get-togethers planned in AA?

Max

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Max Bishop
Brighton, Michigan

Yeah, Hesh, great toot! Thanks for the excellent instructions. I'll try the naphtha test and see what transpires.

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George :-)

Hey Max!

You know we could do that and get together on perhaps a Saturday when there aren't 110,000 screaming football fans in town for a home game.

I'll work on that and thanks for the thanks on the crack repair as well. Knowledge is worthless unless it helps people ya know.... Didn't Edward Snowden say that.....

You bet George and the naphtha thing is a good tool too to show clients that the finish is the only thing that cracked and I've deployed the naphtha just for this purpose before and the clients appreciated that I did.

Update: I set up a light and mirror for inspection and then brushed naphtha along the seam. After letting it soak for a few minutes there was no sign of anything seeping through on the inside. I then flexed the top several times with my fingers, thinking that might help the naphtha migrate deeper. Still nothing visible on the inside. So, I guess this is just a case of there being enough movement along the seam to create a split in the varnish finish? Perhaps my finish ended up a little too thin? Unless you fellas recommend I do otherwise, I think I'll just leave it be for now and check for further changes over time.

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George :-)

Good going George. What I do is use an eye dropper to drop the naphtha all along the crack and then look inside pretty quickly since the stuff dries at light speed. If you still don't see any wetness on the inside the crack is not all the way though and likely not even a crack.

If this is the case it could be that the finish cracked and/or the glue line sunk in a bit and was visible and that split the finish.

You most certainly can leave it as is if the crack is not really a crack and that would be fine. I might be inclined to throw a cleat or two in there anyway knowing as we do that this joint may have some movement. But you could be fine as is too.

One of the early OM's that I built did exactly the same thing and the glue line sank, was visible, and split the finish. No wetness comes through that one either and I just left it alone and it's been 8 years now and no problems.

BTW naphtha is great for removing gunk from maple fret boards and anywhere else on a finished guitar. Good stuff!

Yup, I was rushing off to a family gathering earlier and didn't take the time to state my intentions clearly. I am indeed going to add a couple of cleats at this time and then keep an eye on things.

Thanks so much for the help!

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George :-)

Don't want to hijack the thread, but that would be great, Hesh. Lemme know.

Thanks,

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Max Bishop
Brighton, Michigan

Will do Max! Apologies from me too to George for the high-jack.

All I can say is I'm glad we're not getting charged Luthier school fees for reading all of the excellent instruction and advice on this forum!

What a great tip Hesh.

BTW, I bought a small fiber optic camera that's on a 15' lead and plugs into a USB port. Cost me less than $25. I has leds for light and was intended for plumbing use, but it is a great thing to stick in a sound hole with the laptop set up next to it. You can see more than with a mirror and a flashlight. I don't have anything to try it on, but you might be able to put it through an F hole.

Thanks Allan and very much appreciated!!

The camera should be very useful and we use something similar that originally started life as an X-Box camera and was modified for our uses and held in place with of all things Silly Putty...

Nuttin' wrong with silly putty....