Cracks in back

[bjmsteve]

I closed the box before Christmas. Ziricote and spruce from John Hall. I have been unable to do any further work because of bad weather here in Brisbane with floods/rain 100% humidity.
we have had a few dry days and I discovered cracks along the grain on the back - one from the end of the lower bout to the lower brace and another shorter one in the same spot on the other back plate.there is also a tiny separation of the top central seam on the lower bout but this seems to have been controlled by a cleat I put in as a precaution having had a similar problem in the past.
I would like your input on the best way to repair these. I guess its a good time to find the cracks. I have not done any sanding/finishing yet.
Thanks
Brian

[Tspaxton]

Hi Brian...

Greetings from Cottage Grove Oregon!

I don't know if it's the best way to deal with cracks like those, but I use CA (super) glue. I seep the CA glue into the crack making sure the edges of it are in their original position. I've had good results this way.

TS Paxton

[Kevin Sjostrand]

How much change in humidity did you experience?
You may need to re-humidify to close up those cracks BEFORE you do any gluing and clamping. Also, you won't want to use superglue on the top.

Kevin

[bjmsteve]

over the past few weeks the humidity varied from 100% to 54 %
Today 64 %
I feel the top would close with increased humidity but one of the cracks on the back may need some form of fill.

[tippie53]

This is painful to see this happen . You need to be aware of RH when you glue things up . I glue tops and backs below 50% rh Preferably at 40%. This allows the plates room to shrink without pulling themselves apart . If you are not sending a guitar and keeping it for yourself try and glue up in lower RH times .
If that isn't possible you can "cook" the top for an hour at 220 in an oven to help pull excess moisture out . Be sure to keep flipping it so it looses moisture on both sides evenly . You can rehydrate this and CA it . It may hold for you. Trust me, this happens to all of us once in a while .

[bjmsteve]

thanks
the pictures are maybe a little deceptive.The box is already fully closed.
As the current RH is 60 % I do not think rehydration is an option as I imagine it would just re crack again as the humidity falls.
What is the best option for filling the crack from a cosmetic point of view.

[bjmsteve]

correction current humidity 94 % at 23 degrees centigrade!
I cannot honestly say what the humidity was when I glued on the back but it was normal for here in the sub tropics.
we have had unprecedented rain for 4 weeks. Its only since it stopped that the cracks appeared
I feel that the ziricote is particularly brittle compared to the other few builds I have done with mahogany , cypress and rosewood, and granadillo.
Any suggestions on repair.

[Kevin Sjostrand]

Brian,
Where are you located? How much of the year is the RH over 65%?

Kevin

[naccoachbob]

Kevin, he's in Australia.
Hope the flooding there stops quickly and recedes for those folks.

[Freeman]

Several years ago I learned a good lesson in humidity and humility when my daughters little parlor split wide open (it makes a sickening sound too, let me tell you). Here were a couple of threads I posted back then

http://www.kitguitarsforum.com/archives ... 73_0_2_0_C

http://acapella.harmony-central.com/sho ... tle-guitar

Since then I've repair a couple of other cracks. One of the neat tricks is to use very strong magnets on the inside and out to do the clamping - I bought a couple of the 1 inchers and simple counterbore a hole in the cauls for the magnets

http://www.stewmac.com/shop/Tools/Clamp ... xsr=9.4299

Note that the repair was done in 2008 and has been completely stable since (but we do really good humidity control on that and all my other guitars)