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I'm in the finish stage on an acoustic. A mahogany body with a water-based stain. I put a coat of Royal Lac shellac over the stain (once it had dried). I haven't done my pore fill yet. Can I use West System 3 epoxy OVER the Royal Lac coat? Then once the pores are filled I'll build up more coats of Royal Lac doing a French polish.

Any bonding issues?

The quick and easy, though heartbreaking, answer is NOPE. Shellac will bond to epoxy but not the other way around. So you'll have issues with your pore fill.

Ok. That's fine. I have other pore fill options.

So when you dye the backs/sides, but have light (herringbone) purfling, what is your method for keeping the purfling from getting stained when applying the epoxy pore fill? Do you do a light sealing coat before you really start dragging/mashing it around?

Just to mention: Royal Lac doesn't act exactly like regular shellac and might not be the best to seal with. I believe that when using RL it's suggested that you seal with either their Seal Lac or regular de-waxed shellac.

I know that, with the way it cross-links and hardens, it's not repairable the same way regular shellac is after it's cured: new coats don't burn in and you have to scuff sand for a mechanical bond to re-coat/repair (again, that's after it's cured). Not really sure but I wouldn't be surprised if something related to those characteristics may contribute to it not being the near-universal sealer/tie coat the regular dw shellac is.

IDK if it'll cause you any problems or not but thought it was worth mentioning.

I have done this with maple binding and cocobolo. It took a bit of extra time but I first applied a thin layer of epoxy using a rag over my bindings and the center strip in the back. I let it cure a bit and proceeded to pore fill the rest of the guitar. After the first application I do not get color bleed.

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Thanks!!

Question. Why does the order matter?

I don't use much shellac anymore but my understanding is that it has great properties of making mechanical bonds to pretty much anything, when wet. The same can't be said for epoxy. Since the shellac is dry (when it goes down as a sealer) the epoxy has problems bonding to it properly. In the reverse situation, the epoxy is dry and the shellac can mechanically bond to it just fine.