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One of my current builds is an Aussie-themed dreadnought. The top and bracing are Lutz spruce, but all other components are Australian timbers. The back/sides are blackheart sassafras (Atherosperma moschatum) from Tim Spittle (http://australiantonewoods.com/) -- see the picture below. While dramatic, the wood is fairly soft, and some areas with fungal staining even more so. It doesn't strike me as a particularly good surface for the inside of a guitar.

My proposal is to treat the inside surfaces with a warmed mixture of West System 105/207 to seal and harden the surface. I'll sand that down, essentially to wood, leaving only the epoxy that penetrates the surface. Question is: will braces glued with Titebond Original adhere properly to this epoxy-contaminated surface?

Of course I can and will do some tests with offcuts. Using epoxy to glue the braces is another possibility, although I'm not keen on that. Hopefully someone has tried this before and can confirm that it is viable, or a really dumb idea!

Tim, It's hard for me to imagine that working very well. But, if it's sanded down and there are enough wood fibers for the titebond to grab hold of, then maybe. Pretty wood BTW.

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Jim Watts
http://jameswattsguitars.com

I've never tried that but...

Essentially you want to pore fill the inside before working? Might you not be better off to build it, then give it a good shellacking before closing the box?

Why not flood with thin CA? I'd think it would penetrate better.
As to whether or not TB1 will stick, I think you'll have to run some tests.

Yes, CA would perhaps penetrate even better and be a good alternative, if it wasn't already known to stain BHS. Of course, epoxy might do the same, as it does to kauri. Another reason for testing.

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Don't know that shellac would be nearly as effective at reducing damping of the soft surface. I was hoping epoxy would make for a much harder surface.


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That would be my suggestion too. It should help quite a bit, and lots of people - including me - do it anyway sometimes. Save the warmed epoxy for the outside of the box. IME this alone will be helpful with crackly or otherwise suspect wood.

Shellac is harder than epoxy.

Well you described your conclusion pretty good with "epoxy-contaminated surface."

Basically, the way me reading it is ...you wanna seal off the back...
Ya sure ..ok...if thats your bottom line...then build the sucker and before gluing down the top, slap down some epoxy or if you really wanna seal off a hard back then, carbon fiber imbedded in epoxy and be done with it.



Now since your committed to doing tests...why you wasting both our time and yours with this question ...you tabulating responses that may taint your tests?

Viability and or really dumb ideas are personal bias or persuasions.

Me most humbly suggest that you ...

"Do what thou wilt and then you will know....what works for you."

Then once you've done did it...if your so inclined...let us know how it worked out ...for you. Me sure some of us here would be very interested.


blessings
?adma

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Audiences and dispensations on Thursdays ~ by appointment only.


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Why not epoxy coat the back and sides after assembly as some people do with shellac? Use epoxy thinned with alcohol so you get better penetration and less build up.

Epoxy the inside of the plates to fill pores and voids, then thickness sand down to bare wood. It seems to me that there would be no less wood-to-wood contact than if pores were left open. Finish up with shellac before closing box. Is this an option?

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Doug

Don't let fear or common sense stop you from trying to build something

I will be interested in the results of your experiments. I have some spalted maple which, if I ever get around to building with it, I have planned to harden with Smith Penetrating Epoxy. This material is designed to strengthen rotted wood, and is supposed to penetrate into punky areas. I am sure it will affect the color, but you can't have everything.

I'm not sure how well regular epoxy will penetrate wood. CA will penetrate will, but I'm not sure about how strong it will make soft porous areas. People often speak of soaking wood with glue to make it stronger but I've never seen any tests. This Smith epoxy does work well on rotted wood . . . spalt is rot . . . therefore I think it will work . . . I think.

In terms of gluing, I would expect to use epoxy to glue wood previously treated with epoxy, but I wouldn't be surprised if Titebond adhered well--I'd test with off-cuts.

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Tim Allen
"Never hurry, never rest."

Best results will come from gluing up prior to applying epoxy/shellac/CA or whatever you end up using. By applying sealant first and sanding down to expose wood fibers you're only making a bad situation slightly better. PVAs such as TB will not adhere well to such sealed bonding surfaces. Epoxy will generally bond well with itself, but will benefit from being joined before becoming fully cured (simply because more un-reacted chains will be available for bond formation.) You can save yourself time and headaches by gluing up prior to sealing the wood. If you absolutely insist on sealing the wood first, at least mask off the bonding surfaces and lightly sand them if necessary.

From industry experience I can already confirm for you that Titebond does not adhere well to dried films of PVA, epoxy, CA, or shellac due to the fact that in order to develop bond strength it must lose moisture and have close contact to a substrate with suitable surface energy (which the proposed sealants will not have.)

Glad to see you're still about Hugh. You've confirmed what I feared, so I'll modify the plan accordingly.


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Is it? Never woulda guessed that.


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The fungal staining is a form of spalting. I've worked with some spalted woods before, some very heavily spalted, and you're correct that it is soft. But, No need to seal the interior of the guitar, really. I'd suggest that you go ahead and build it in regular fashion, but perhaps apply your thin, warm WEST epoxy coating from the exterior, after you're completely done with the soundbox. Much like those who use epoxy as a pore filler would, except that you will -want- it to soak into the wood as much as possible. This should help strengthen the wood as much as it would if you applied it from the interior, yet it still leaves the inside of the guitar raw and unfinished so the wood can breath a bit, and making any future repairs simple.

WEST epoxy original stood for Wet Epoxy Saturation Technique. I don't remember if their current formulas are still meant to penetrate and saturate as deeply as the original, so look into it a bit; there may be a version of their's(or someone else's) that is specifically formulated for the task.