Bummer......My Top Is Cracked!

[Darryl Young]

Wow, finished my buffer and buffed my guitar this afternoon. It was warm here today.....over 70 and much more humid than it has been. I had the guitar out in the garage while buffing then returned it inside the house. It's warm enough in the house that no heat or air conditioning is running.

Anyhow, the crack is right down the center seam.....right where the bridge will be glued. It's probably a good thing it's in that location I guess since it will have a giant cleat (the bridge) glued over the top of the crack. Any thoughts on how to address this? It's about 2" long. The finish is split there for the length of the crack. Actually, all I can see or feel is the finish crack......but since it's exactly down the center seam, it seems the glue line mest be pulled apart slightly. My finish is very thin on the top.

I try showing a picture but never could get a good shot of what is going on. I place red arrows at the start and stop of the crack.

PointersToCrack.jpg

[Ken C]

Do you still have any radius to the top? With the x-brace just below and the bridge backing plate at the lower end, seems like getting a split in that area would be unlikely. Man what a bummer. Did your glue joint fail or is the split along a seam running parallel to your glue line? Did your braces, bridge backing plate, and top all have the same moisture content when you assembled them?

Ken

[Darryl Young]

Ken, I can't really say for sure the top is split......but the crack in the finish runs perfectly down the centerline seam so I assume the seam is partially seperated. I can't feel any hint of a a crack from inside. Appears the crack starts 1/4" or so above the bridge plate and extends below the bridge plate 1/2" - 3/4". I controlled the humidity when glueing the braces to the top. Glued all the braces at about 38% - 40%. And yes, there is still a nice radius in the top.

[tippie53]

you need to probe the top to see it if cracked . I doubt your top is cracked . That usually happens with lower RH. What glue did you use ?

[Darryl Young]

John, you glued the center seam so I assume it's Titebond. I used fish glue to glue the bridge plate in place and all the bracing.

How do I probe the crack.....with a needle or something? I agree with you that going to higher humidity shouldn't open a crack. I just tried a 0.0015" feeler gauge. I couldn't even get it in the crack in the finish. It's very small....but you can feel the finish crack with your fingernail (and see it in person but it doesn't show in the photo).

When I have the bridge ready (hopefully tomorrow), I'll mark and remove the finish and see for sure what is going on. If it's a finish crack, that does not bother me. The more I think about, the more I suspect that John is right that this is likely not a crack in the center seam. Hopefully, I'll let you know something tomorrow.

[Ken Hundley]

I have dripped a little water on a crack, then push on the crack and see if you can see the water bubbling out when the crack moves. You could repair this invisibly with hide glue. If you have no hide glue, you could use knox gelatin, which is nearly the same. I have glued a fingerboard on witht he stuff and it has yet to show any signs of release. It wicks in, wipes off with warm water, and is great stuff. Check out Frank Ford's comments on using it: http://frets.com/FRETSPages/Luthier/Tip ... nglue.html

[tippie53]

water or nephtha on the crack is good . A probe is a dowel so you can get deep into the body / just pushing along each side of the crack if it is open you should see movement . I would use naphtha as it won't interfere with the glue . If you have a crack , you will see a wet spot along the seam .

[Ken C]

Can't you put a light bulb or something inside the guitar and see if any light escapes through the split? I'd do this before poking holes in the finish. You may not have a crack at all. Your finish may simply have shrunk along the seam, allowing the seam to be more visible.

Ken

[kencierp]

Ditto Ken C --- Put one of those little LED flashlights inside and go into a dark room.

[Darryl Young]

No light comes out of the crack in a dark room. Not sure what this tells me........seems a closed crack wouldn't let light through. I located the bridge tonight so maybe I can remove the finish tomorrow evening and will be able to determine if it is just a finish crack or if the wood has cracked. Likely it won't be an issued even if the wood is cracked since the bridge plate is on one side and the bridge will be on the other.