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JouniK

Burl void filling, stains and oil finish

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Hi,

Suggestions for methods of filling poplar burl (1cm thick drop top) voids when using water based stains and an oil finish? I am pretty new to building guitars and wood working let alone working with poplar burl and was wondering how would you guys treat the wood when option is to use water based stains and an oil finish. I want as much as possibly to highlight the wood textures with stains and use an oil finish. How do I minimize the affect of filling the voids with glue etc. to stains or oil finish?

I have read about filling the voids with epoxy/CA glue, CA glue + wood dust/coffee grounds or let the voids open. Any pros or cons to these?

How about sealing the grain?

20190902_153826.jpg

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Hi JouniK and welcome to the addiction!

There's many ways to skin a cat. One option would be to apply dye to the glue+dust mix but that might cause issues if you want to fade from one colour to another like on a burst. Anyhow, wood glue like TiteBond might be better than CA since it has a longer open time and doesn't change the colour of the wood dust when drying.

Coffee grounds? That might add a pleasant smell, especially for us Finns!

Are you 100% sure you want an oil finish on the burl? Poplar is pretty soft by itself and the burl is even softer at certain spots and porous as a sponge! For a decoration on the wall that'd be no issue but if you want to gig with it, lacquer would be much tougher. That would also make filling the voids much easier.

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I chose oil finish so that it would be as "organic" looking as possible. Yeah, I noticed that burl is pretty soft and porous but thought that several coats of oil would make it tougher enough. Do not like much about laquer or poly finishes. And because I do not have equipment or separate place to spray those on so those should be wipe-on products.

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Highly understandable. Half of my builds so far have an oil finish. Then again, I don't gig and the woods aren't exceptionally soft.

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I have a bottle of titebond original. if I mix that with dye+sanding dust would that be too stiff to get exactly to the voids? Thinking that can I get the excess off by sanding from pores around the voids to accept stain and oil again or would that be even an issue?

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Any suggestions on how to get the wood more durable by still using the finishing oil I already purchased (Crimson Guitars Penetrating finishing oil)? Mix in a bit of shellac maybe or add something else after the oil? Earlier I was looking into Danish Oil but read about the bad odor it has and disregarded it as valid choice.

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I'll give you one piece of advice I wish I'd been given before I did a mapa burl top... If you are going with a dark (black) fill for voids... you should use it to spot fill the bigger voids and then use clear and go over the entire body.  I used black epoxy and and went over the entire top and it doesn't look bad (it was a gotm winner in 2018)... just a lot of unfortunate smaller voids got filled with black and that kind of took away from clean look of the mapa. 

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Good point there about staining the entire surface with a dark fill, @mistermikev. I had the idea about a dark overall filling but didn't think it could smudge the surface beyond normal sanding when leveling the filler.

Adding dye to Titebond+sanding dust should make the mix even more fluid unless you're using something like Herdin's Petsi powder. Even then it's just a matter of proportions, just add glue or even water. Bear in mind, though, that the more fluid your filler is the more it will shrink. Also painting the voids with water might help the filler mixture grip and go deeper as the water will absorb into the pores and suck the filler into the void.

Another thing to remember is that wood gets darker with UV light and knots even more so. Thus it's recommendable to make the filler very dark. Black may have a wrong type of hue if it is of the bluish type, a very dark brown might be closer to what the burls will become. The best might be to mix some brown or other red related dye with the black. As a Finn you've seen cheap pine furniture filled with "matching" pine coloured stuff which will shine pale after the surrounding wood has darkened. You can't go too dark with filling knots and burls.

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I'm going to dye mine a dark brown, sand it back, fill the voids with Z-Poxy, sand back some more, go into my dye routine, and finally seal the whole thing with polyester.

SR

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How would the oil finish look when voids are filled with epoxy or glue+sawdust since it does not sink into those? Would it look odd? I am now planning on doing my own oil+polyurethane mix (like danish oil) to get a bit of a film build up on top of the body. Probably that would add more durability and look more consistent when voids filled with epoxy etc. I probably have to do some test of my own with the little left overs I have from cutting the body plank. I hope I have enough of the oil and stains to do those.

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Typically voids,  pores, cracks and so one get darker with oil. The same thing will happen with  epoxy or other fill agents. It is another reason for choosing dark fills, so it looks natural. So with epoxy or CA you void looks very much the same as if you did not fill it and just oiled it. The filled area will tend to look glossy when finished. If you are going for a gloss finish it blends in, If you are going for a more satin finish the voids will tend to stand out, which really is not a bad thing either. They become a feature.

SR

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