How would you repair this?

[Joralin]

Hello Guys,

I bought a nice Ukulele with a little problem.

The two back pieces (solid wood) are separating and there is a small gap all along the back of the instrument.

I heard that is happening mainly because of dry and shrinking wood.

Since the top is not sunken in ( and if, just very slightly) and the fret ends are not very sharp I'm not so sure if humidity caused this.

How would you repair it? (Glue, technique, etc.)
Would you first try to hydrate it?

url=https://ibb.co/8PCc4b1]

[/url

 

[John Colter]

I bought a lovely solid Koa uke with very similar separation problems on both front and back. I believe it to have been caused by shrinkage. Just leaving it overnight in the kitchen, where the humidity was a bit higher, reduced the gap visibly, but not entirely. I then used ordinary white carpenters glue. This is easy to work with and wipes clean with a damp cloth.

CA glue is very good on closed, or almost closed, cracks - but it can make a mess of the finish.

On the inside, I glued a strip of wood (1/16" thick and about 1/2" wide) where I could, working through the sound hole, of course. Down beyond the bridge, I couldn't reach.

I bought some small circular magnets which are very effective for holding patches in place while the glue dries. These need careful handling. They are very powerful!

The uke is now really sound and the repair can only be discerned with close inspection.

Best of luck!

John Colter

ps. This photo makes my repair look much more obvious than it appears in real life!

 

[Joralin]

Thank you for your help.

Do you have a photo from the strip at the inside?

Does it makes any difference what type of glue i use? I guess some glue could be too stiff (for example Epoxy) and cause cracks at other posotions while the wood is moving with humidity and temperature.

Is there a way to close the gap with some clamps while gluing it?

 

[John Colter]

Don't try to close the gap with clamps, that's a No, No! I would shut the uke in a hard case with a (piece of) wet sponge, overnight in a warmish room. That should cause the wood to expand as much as it is going to.

Use ordinary white woodworking glue. It gives you plenty of time to work with before starting to dry off, and it cleans up with a damp cloth.

I've remembered that the strip I used was made from Mahogany veneer, so it was more like 1/32" thick, and I cut it with the grain going across the width, not along the length.

The uke is an Ohana SK300G. I made the repair more than ten years ago. This uke is one of my favourites.

If you use small magnets to hold things in place, put a piece of thin card or thick paper between the outer magnet and your gloss finish! Carefully!

John Colter

 

[John Colter]

I should add that if you are hoping for a repair in which the gap is completely closed and the appearance is as new, that is not a reasonable expectation. Just do the best you can and accept the result. The repaired gap will probably still be visible, on close inspection, but the main thing is that the uke should be solid and stable. The way it plays and sounds will not be adversely affected.

John Colter

 

[Joralin]

Thank you very much. Yes I know it will be visible, but this Uke is a players instrument .

The only bad thing is that I have no color matching wood for the inside, just a block of maple.

But I would live with that color, some good guitar luthiers also use lighter wood for their "middle stripe" to create a nice contrast at the inside.

I guess I should use veneer over solid wood, because it will not shrink or expand?

 

[John Colter]

"I guess I should use veneer over solid wood, because it will not shrink or expand?"

I'm not sure what you mean by this. By "veneer" I mean just a single layer of very thin, solid wood - I haven't measured the thickness but the stuff I used was no more than 1/32" and quite possibly less. A friend, who is a keen woodworker, gave me several small sheets. I find it useful for making small cleats when repairing cracks and splits.

John Colter

 

[Joralin]

Ah okay, I thought you mean laminate wood.

 

[Kelali Kev]

If you are going to add a patch on the inside along the seam, the wood strip should be cut against the grain so that the grain runs perpendicular to the seam. The strength of the patch is then with the grain holding the 2 halves together. If you run the grain of the patch in the same direction as the seam then it is just as prone to cracking along the seam again. Spruce or mahogany or even cedar are easier to work with than your maple and the patch strip can be relatively thin.

 

[Joralin]

Good to know, thanks