Crack repair

[Masato]

I'm trying to build my #1 guitar now.

After installing binding, I noticed that there is a crack on the spruce soundboad.

It is lower part of the soundboad, near center joint. About 2inch long.

Crack is not very deep, but it seems it has dirt and looks very bad.

I was very shocked... really...

Crack was there when I noticed, so I have no idea about when and why it happend.

Maybe it is because of low humidity. Roughly always, my room is about 50% humidity conditioned though...

I would like to know how to repair it.

Any advice and suggestions will be greatly appreciated.

BTW I did shellac finish once to avoid chipping and scratch during binding process.

Thank you.

Masato

[mirwa]

There are many reasons why the crack could have appeared, but really its more important in getting it fixed.

As its a guitar you built, I would enquire as to your bracing layout internally before giving a repair recommendation.

How long was the top fitted before you noticed the crack, hrs/days/weeks or months

Any chance of some photos of the internal bracing.

Steve

[Masato]

Thanks for comment.

Bracing layout is normal OM style pattern.

I fitted top about 1 month ago.

Thanks.

Masato

[mirwa]

Nice clean work on those braces, off topic, why rosewood for the bridge plate.

I was concerned maybe an unconventional brace layout accompanied with some sides that wanted to flex now that they are out of the assembly mold, were the cause of the split.

As the wood is still raw and the build fresh, I would attempt to clean it, using steam, there are other ways of cleaning including alcohol / lighter fluid.

Increase the humidity of the guitar (slowly and over time) and see if it closes up, if it does then glue, I am a fan of cleats internally but many others are not, that's your choice what to do, if you use a cleat or two to stabilise it, smooth all of its edges out and make it a low profile, almost like an upside down dish.

It's likely that when you routed the edge to do the binding, it caught and split the end grain, real easy thing to do.

Steve

[Masato]

I'll put your advice to good use. Thanks a lot.

Masato

[Ned Milburn]

If the crack is humidity related... if you are at a constant 50%, then increase the humidity, then glue the crack, then the humidity goes back to 50%, then the original shrinkage stress re-enters the wood, with possibility for a subsequent similar crack near the original. This is why I don't recommend higher than standard humidity to repair cracks.

You can easily massage some AR glue into the joint (I'd recommend from the inside if you can reach) with your finger tips. Clean up with a slightly dampened cotton ball. Everyone has his/her own glue preference. I prefer slightly thinned TB2 for this use, since when dry and set (longer than 24 hours) it is truly "stronger than the wood itself" as per its advertising, and it dries without becoming brittle. Cleats are optional.

[pops]

If you can get a dry spruce plane shaving in the crack then wick in hot hide glue you will not need to cleat. The end block will stop further cracking and will also not allow it to close without a higher humidity, which you must maintain or it will open up again. Since you are already at 50% unless you plan to keep it at a higher humidity I wouldn't just swell it and glue it. If if opens up later and it is cleated, you will have to get the cleats out to reglue or they will hold the crack open.