Cocobolo rosette nightmare

[wadkin]

Okay so I made this segmented rosette out of back & side Cocobolo off cuts, it came out well all the joins looked good was very happy with it. A couple of months after finishing it something weird has happened, the joins have now become very visible. Rather than the joins becoming sunken in-between the segments, as you might expect if the segments shrunk they are in fact raised. Now between the joints there are raised creamy/yellowish ridges.

When making the rosette I wiped the segments with Xylene before gluing them in with Titebond Original. Over a month later I later sprayed on one coat of shellac and two of pre-catalyzed lacquer. I know Titebond isn't much cop when it comes to Cocobolo, but this is almost as if it's like oozed out between the joins like some sort of horrible puss or something. I'm wondering if like there's a reaction happened here or oils have seeped out of wood or what?
I'm totally stumped by this, my prize guitar now looks awful seems like there's little I can really do but what went wrong?


Weird nasty yellow raised joins :@



Original rosette all joins look good ect.

[pat foster]

Dang! I hate it when that happens.

Sorry I don't have any advice. I had that happen on one of my first guitars, using TB on my rosette where my joints weren't tight enough. It looked great for months, then the glue swelled. I still have the guitar and the problem is still there. It still plays well and sounds pretty good.

Pat

[curly]

It's just a matter of cross grain shrinkage me reckons , your rosette is built out of cross grain tiles . If you add up the combined shrinkage of the pieces it would easily account for the white lines .

[wadkin]

Yeah initially I thought it was shrinkage, but how can this be if the the joins are raised makes no sense, indeed it is like the glue has swelled up. I'm wondering if perhaps this swelling wouldn't happen with epoxy. I suppose I could pop the pieces in the oven for a time to dry them out next time. It just seems wrong that the glue swelled up between the joins it should be hard.

[dshaker]

I wonder if the Titebond could be absorbing a solvent from the cocobolo and expanding itself and the parts of the cocobolo it is in deep contact with. It might be worth asking the Titebond people.

If it was me, I'd use black epoxy the next time I did a cocobolo inlay.

[dshaker]

I emailed the technical support department at Franklin Glue, the makers at Titebond. They said:

It sounds like and appears that you have a raised glue joint. How long did you wait after gluing up did you sand and finish the guitar? Titebond Original wood glue is water based glue.

1 ) Glue is applied and pieces are joined.
2) Moisture in glue causes localized swelling.
3) Panels are planed smooth before swelling goes down.
4) Swelling goes down, after planing, leaving a depression

So it appears they are hypothesizing that you leveled the cocobolo too soon after gluing it in and, as a result, took too much off the middle of each inlaid piece. As the wood lost moisture from the glue, the center of each piece shrank more than the ends.

Does this seem plausible?

[kiwigeo]

Thinking aloud here and it may not be a practical fix but here goes anyway:

1. remove finish from rosette area.
2. pumice and meths pore fill job on the central part of the rosette (FFFF grade pumice applied with a mini ponce) . The meths should pull colour out of the cocobolo and stain up the glue and also fill the pores.
3. Refinish area.

[Mark Fogleman]

Just a SWAG but when you originally glued up the rosette how dry was the workplace? If it was dry then and now (mid summer) when humidity is high, you may be dealing with swelling of the Cocobolo. The radial design multiplies any swelling times the number of joints. This could stress the joints and lift them. I know glue creep is controversial, but this may also be part of the problem.

Try to dry it out for a week or so and see if the problem goes away. If it does you may want to create a .02 or so strip of black Epoxy between each tile of Cocobolo to act as a compression joint.

[Kim]

As to what caused the issue I think it was probably a combination of things...Cross grain shrinkage as Curly suggests, perhaps a variation in RH, and the simple fact that a spruce substrate will expand and contract with changes of RH far more quickly, and to a much greater degree than 'nail hard' cocobolo could, probably all worked together against you. Anyhow what's done is done so I would try making a template to carefully rout the glue joints so they can be inlaid with the same purling used to define the circumference...worth a try anyhow.

Cheers

Kim

[wadkin]

Thanks for all the replies I have been away. Yes I think it is the spruce swelling due to increased humidity. Indeed probably the only solution is to strip the varnish right back not so easy with Pre cat varnish but perhaps I will bite the built at some point. Might think twice before doing a thick hardwood inlaid rosette again.

[peter.coombe]

Might think twice before doing a thick hardwood inlaid rosette again.

I wouldn't go that far, but would modify the way you did it. I had a similar problem on my 4th guitar. The wood in the rosette moved across the grain and since the grain was at 90deg in part of the rosette to the Spruce there was a problem. Is a dumb idea to install a rosette with grain and movement happening in different directions. So, after that all my hardwood rosettes have the grain running in exactly the same direction as the Spruce. At least then everything moves in the same direction, although not necessarily at the same rate. You then have more of a fighting chance that it will be ok. Your rosette is about the worst situation with the entire rosette expanding and contracting across the grain. Add it all up and there is going to be a fair bit of movement, and it won't correspond to the movement in the Spruce. So far so good, the problem has not re-occurred in any of my later guitars.

Peter