Official Luthiers Forum!

I've had a lot of questions on the application of the
epoxy, and it is a bit tricky. I've updated my finishing
instruction page with more details, see
http://www.DoolinGuitars.com/waterborne/instruction
s.html. In brief:
1) Use SB112, not Clear Coat. Clear Coat will work,
but it's rather thin so it needs more silica and more
coats.
2) Measure by weight with a gram scale, not volume,
and mix really well. 100:44 is the ratio by weight for
SB112, 100:43 for Clear Coat. Hang the guitar to
cure in a warm room, preferably 70 degrees or
higher.
3) Squeegee it on so thinly that you don't have to
sand much, if at all. But don't sand back to bare
wood either, you want the surface to be wetted with
epoxy for good color and adhesion.

Mike Doolin

So Mike you are using no silica or microbeads with the SB112 if I read you right?MichaelP38475.7359490741

Here's a clickable link

Thanks for that page, Mike.

Mike,
Your site says that you should not use shellac over epoxy because they won't stick to each other. This is interesting to me, because I have seen a number of other folks suggesting the opposite --- namely, that one should put a shellac washcoat over epoxy because the epoxy may not bond well with the lacquer or other finish. Have you had problems with shellac adhering to epoxy? If so, is it just System 3, or have you experienced problems with other brands of epoxy as well?
Thanks,
Kelby.

I fill with Epoxy and then french polish. It seems to work great for me. I am using a thinned Epoxy (10% thinner)

Michael P: No, I still use silica thickener (never
microbeads) in SB112. It just takes less of it than
with Clear Coat.

Kelby:Yes, I have had catastrophic problems with
shellac adhering to epoxy. I don't know about
adhesion between epoxy and lacquer, but I do know
that if you seal with epoxy, then spray a washcoat of
shellac, and then spray on the waterborne, the finish
will peel off like a grape skin.

I've used epoxy as a sealer/filler under rosewood
sealer and then polyester, and it adheres to that well
too. I think the key is to spray the top coats within 24
hours of applying the epoxy, while it's still slightly
tacky. That allows for a chemical bond between
them.

The way to tell is to do an adhesion test on any new
combination of finish products. Apply the finish to
sample boards of spruce, mahogany and rosewood.
Let cure and rub out as usual. Then just beat the
crap out of the samples: hammer them, cut them,
drill them, chisel them, do anything you can to try to
get the finish to separate from the wood. If it holds,
you're good to go.

Mike...Your recommendation to do an adhesion test is the best advice.

I recently sprayed Target's 9000 waterborne over epoxy (Zpoxy). Jeff Weisborn (tech rep)of Target later told me I should have sprayed shellac over the epoxy. He contends that the bond is mechanical and that a chemical bond is only possible over shellac. Perhaps the 9k is significantly different from KTM-9.

Bottom line...I'll test as you suggest before using any finish.

_________________
JJ
Napa, CA
http://www.DonohueGuitars.com

There are so many different finishes,epoxies, and finshing techniques out there that I think you have to become a skeptic and prove to yourself that the system you are trying will work. To me this means taking with a grain of salt whatever you read on forums or hear from product reps. As the saying goes your results may vary. Even small variations in methodology can yield unexpected results.
      For example the finishing method I use now is Z-poxy over french polish, I had no idea if this would work so I applied it to several different types of wood scraps. I torture tested the samples thru cycles of hot/cold/humid/dry conditions before I even tried it on a guitar. Matter of fact the first one I tried it on is up here on this site in the Luthiers gallery.
        Forums (especially this one) are great places for methods and ideas but is no substitute for that grey matter between our ears.