MIMF

Hey guys, I'm doing a rather elaborate marquetry inlay in the spruce top of an acoustic guitar. It is composed of many pieces of dyed veneer that is 1mm thick.
things are going very well so far.
I need to determine the best glue to use that will hide slight gaps, and hold all these bits in there.
I will be sealing the entire cavity with shellac once everything fits.

My first through was to use fish (or hide) glue for the natural look against the spruce. But it won't fill gaps without drop filling in after it shrinks back.
So, the next thought was epoxy, but it will be very clear and may show gaps.
Also thought about mixing some spruce dust into the epoxy to see if it will look more natural - tho i expect this to get darker than the natural spruce surface.

This process is long enough, so I'm trying to avoid doing a bunch of experiments to find what i like best.
Anyone have any wisdom to share?

Shrinkage! (Apologies - irresistible Seinfeld reference.) I'm definitely not good at inlays and rosettes so ... grain of salt and all that ... but if you want to know how things can go wrong ask somebody who makes lots of mistakes. I did something like that with pieces of very thin burl veneer using hot hide glue. Not so good. I glued pieces of veneer tightly together and came back a couple hours later to find 1/2 mm gaps. Yikes. I guess they soaked up water from the glue very quickly and lost it almost as quickly. Personally, I would try the epoxy.

No wisdom here. I use CA for rosettes, which are thicker, so don't know how it would be for thin veneer pieces. I glue everything together with liquid wicked in, then go over gaps with gel.

I would use the long-set epoxy with a bit of sawdust, but not from spruce because it would be too dark. I would try to find a lighter colored wood and use its sawdust. Holly would be a good candidate. When mixing in the sawdust you need less than you think, at least that is the case with ebony. Don't mix in so much that it becomes opaque. More like a tint. It always dries darker and more opaque than the wet mix looks. To prevent entrained air bubbles, place a bright light over the wet glue, or take a propane torch and flame the surface.

"What ... do you mean like laundry?" - Yes, Bob, I know about shrinkage, and that's what was pointing me to epoxy.
I think Barry & I see eye-to-eye on this. Your description, Barry, is pretty much what i had in mind, and I think I will do one test inlay to try and calibrate my "tint" filler.
Peter, I also use CA for rosettes most of the time, but this is much more than a rosette. CA is great when there are no gaps, but I know that I will have some gaps, and spruce is unforgiving. So i need some reasonably tan colored fill.
thanks for helping guys!!

Chuck, I am sure you know this but I will say it for others that may try this. After leveling the fill you should put a coat of sealer on everything in order to judge the color of the filler and the surrounding spruce under finish. This will be a challenging project and I am most interested in your results.

Chuck Tweedy wrote: ↑Tue Aug 25, 2020 11:50 am
"... So i need some reasonably tan colored fill."

I've mixed bone dust with epoxy for use as a filler. Another problem I have with this is the gaps aren't clean, but often have glue remnants visible at the surface. A collection of dental tools helps get those out but can't say I'm ever satisfied with the results on light colored woods.

Marshall - i agree - there is no way to fill spruce.
My only defense is to cut the cavity as clean as possible, and to fill any bo-bo-s with wood (so far only one bo-bo)

I've heard of using colored pencils to fill little gaps in marquetry and mitered corners on purflings, though never tried it.

Hey Marshall, I don't think I'll be doing that here. Sounds like a shellac stick type fix to me.

If you lay one veneer over top of the other and cut through both at the same time you might be able to avoid gaps (but perhaps you already know that).
https://www.youtube.com/watch?v=Anu1VniA8X0

Chuck,
Is there any chance you could use the technique of cutting an identical trough in polyethylene and in your top, like has been mentioned a few times here for laying up rosettes?
That would let you take your time fitting your veneer pieces for minimal gaps, and then once the whole inlay is done, flood it with CA and install as one piece.
It would have the advantage of stabilizing the veneer pieces structurally, as well as letting you have a layer of CA over the veneer to lessen the chance of sanding through it in later stages of the project.
You would probably need to shellac the edges of your veneer pieces to prevent discoloration of the end grain edges from the CA wicking, just like doing the same to the edges in your top.

Hey guys, thanks for all the advise, but the train has left the barn, the cow has sailed, and the barn door is flappin' in the breeze.
I'll share the finished product some time soon, but suffice it to say that all the cutting, cussing, and consternation has come to a crescendo, and I'm near ready to constrain the crap in its cavity.
so much for my illiterate alliteration and idiotic idioms - i gotta' get back to work.

Chuck,
I've a friend who has done extensive marquetry, and so I called him to see if he had any advice.
He said he has been happiest just using regular DAP wood glue or you can use titebond. He said he has less problems with it than using HHG and hasn't had problems with shirinkage. If you do have shrinkage he suggested going back over the problem area with wood glue with some sawdust of appropriate color.

Below is a link to some of his work...worth brousing some of his carving etc as well.
https://zongkers.com/custom-marquetry/

Wow! I would say that he knows what he is doing.
I'm definitely a rank amateur relative to that.
thanks for asking him, i will definitely consider that - i'll have to do a glue-off test

That's some nice marquetry alright. But that's all hardwood veneers, as far as I can tell. There's a reason why most inlay goes into ebony; it's the easiest wood to hide problems in. Spruce is, without any doubt, the hardest. Any sort of sawdust that you use as a filler will end up darker than the spruce. Some types of hardware store filler will match pretty well, and sometimes you can get away with the standard that violin makers have used for years; lycopodium spores mixed with hide glue. But nothing is foolproof, and the first rule is to practice on scrap. The other problem with inlay into spruce is that the cuts around the perimeter need to be perfectly clean; and compression of the wood will show up.

I may get some of those spores - they are available on Amazon
As you can see from my image, things are going reasonably well. I have all the leaves & buds fit. 3 more flowers to go.

kudos to you for that. It looks great so far.

I've never heard of using lycopodium spores before. That may have been able to save me from enlarging a rossette or two.

WOW Chuck!!
That is going to look spectacular against the spruce.

And your fit sure looks amazing too. Can't wait to see it when done and finish on it. Is this for family?

Clear pick guard?

Really nice so far, Chuck. Can I ask what is the red material.