Official Luthiers Forum!

While reading on LMI's info on their KTM-9, I came across this by Doolin:

Important: do not use shellac over or under epoxy, the two will not stick to one another! Either one works as a sealer and improves adhesion to the waterborne, but it's one or the other, not both. I prefer epoxy because it "wets" the wood better and acts as a filler as well.


What gives? There are tons of comments about using shellac as a sealer, then filling with various epoxies. Is there anything to this, or is it a misprint?

I/ve used blonde dewaxed shellac over a headstock that was filled with epoxy/silica /alcohol to fill the pores. If the shellac is dated, or old it could cause adhesion problems , but then, if it was a thin coat, it can be cleaned with alcohol and sanded back with 240-340. to start over

Lots of people pore fill with epoxy and then French polish shellac over it. Not sure about shellac under epoxy though.

It's not a good idea to put a hard finish over top of a softer finish.

It is my understanding that people commonly french polish over epoxy pore fill. I haven't done it but was intending to do it on my next project (unless I am convinced otherwise here). I have also read that you epoxy fillers will not stick well to shellac sealer coats and that one should sand back any shellac seal coats before pore filling. Again, I have yet to try epoxy pore fill. . .

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Bryan Bear PMoMC

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That's not quite the same, the pore fill is usually sanded back to bare wood, so the only place the shellac would be in contact with the epoxy would be in the pores.

I think the OP might be mistaken about sealing with shellac prior to pore filling with epoxy being a common practice, the sealer should go on after the pore fill, and what I said above applies.

I vaguely remember Mike's original post about the problem, and IIRC it was a specific brand and type of epoxy that had problems with shellac.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

There have been discussions on this before. The consensus seems to be that it is OK to put shellac over epoxy, but not OK to put epoxy over shellac.

I think LMI is simply being cautious. I've shellacked over Z-poxy many times and never had a problem. However, I always sand epoxy fill lightly and scrub it with a brillo pad and soapy water to get rid of the waxy blush first.

Why would you apply epoxy over shellac anyway? Pore fill? LMI microbead pore filler works well over shellac sealer, FWIW.

Back in the day on the OLF we had a member, Michael Dale Payne who is a great guy and was very generous with all of us with his time and more. Michael is the one who created the OLF plans for the OM, small jumbo, and possibly the medium jumbo too. He originally gave the plans to the OLF for distribution to benefit both membership and forum. Later these plans found their way to Stew-Mac. Hundreds of very cool guitars have been built from his plans.

Mike was our resident expert on this question and likely 50 times or more he was known to post a direct answer to David's direct question. It came up so frequently I wondered if he assigned a key to a macro that would make that post for him...

That answer was and is: Epoxy under shellac is fine, shellac over epoxy is fine but.... EDIT: epoxy over shellac should be avoided....


Regarding Mike Doolin that quote is very old, over 10 years old IIRC and this was back in the day when Mike D. was pioneering early waterborne finishes for Lutherie. Mike D. used KTM-9 back then which was sold by LMI hence the instructional writings on LMI's site. I believe that Mike D. moved away from KTM-9 a long time ago.

Mike was keen to only use System III back then and his comment was specific to System III as per Roger's comment.

The only thing to add is that lots of folks, including Mike Doolin would apply a very thin wipe-on coat of thinned epoxy over the entire surface of the instrument's woods that required pore filling (not the top....). The reason for this wipe coat was to even out the color, pop the figure (epoxy pops figure line nobody's business) and you can see from Mike D. quote above he mentions epoxy's figure popping qualities as well.

Many of my guitars have this wipe on epoxy coat too for evening out the color and popping the figure.

So..... if you are hankering to pore fill with epoxy which can work very well by the way and you are keen to pop the figure on your very cool back and side set, neck, etc. with a final, thinned wipe-on coat this coat acts as a sealer as well.

There has been some disagreement about this in the past on the OLF where some believed that if the entire surface has epoxy on it shellac is redundant where some felt like a sealer is necessary. Of the 5 of so of mine that I kept all of them have epoxy pore filler, a color wipe-on coat of epoxy, and then the final finish applied directly over the epoxy - no shellac. All instruments are trouble free and look like new today except for fret wear....

I have french polished with shellac several to date with the shellac directly over the epoxy and these instruments have held up fine except for my personal favorite guitar a 2.9lb hog/euro L-OO that is shellac over epoxy and on this one I have worn some of the shellac off the back of the neck and like it this way. I'm on my way to having a Willie Nelson Trigger of my own.

So the real answer here is it depends. If using epoxy to pore fill and not covering the entire surface only leaving epoxy in the pores a sealer coat is a good idea. If using an epoxy wipe coat many, not all, believe that a seal coat is not necessary. Those that I know who used a seal coat over a wipe coat of epoxy did not use shellac and favored a vinyl sealer and reported success.

Thanks. I tried searching, but as you all know, the amount of hits almost insurmountable, and I couldn't find the right posts.

Greg, the way this would happen is that I spray a thin coat of shellac before binding to protect the wood from glue squeeze out and the binding tape. Then later when I fill, the epoxy would be going over top. I think after reading the comments above, I will definately sand down to wood before filling with zpoxy. I have BW back/sides, and the epoxy does bring it out very nicely. (thanks for advice I got here)

Err ... you might want to edit this Hesh, seeing as it's the most important sentence in your post! Suggest rephrasing in terms of A over B and B over A (in the sequence one would apply these materials).

Yep made me go back and read it a few times.
with 15 builds under my belt over 15 years, I've always used zpoxy fill and french polish no problems so far!

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Say what you do, Do what you say.

Sorry guys must have been starting the celebration a bit early here.....

Happy New Year - Post Edited above....

I agree. I found out the hard way.

I recently re-topped an Ovation 1619 Custom Legend. Because of the method I used, I sealed the top with shellac, then used epoxy to glue the top to the bowl. (Loctite Hysol 0151)

The epoxy that came in contact with the shellac did not cure properly, and hence, caused problems with the lacquer finish applied afterward.

The only way I was able to fix this was to sand the top wood back to bare, then re-apply the shellac.

Thinking back, this makes perfect sense. Uncured epoxy is dissolved by alcohol. Once the epoxy has cured, it is impervious to alcohol, but shellac is not. Obviously, something in the epoxy caused the shellac to dissolve and when it mixed in with the uncured epoxy, it altered the epoxy and prevented it from curing correctly.

I will still use epoxy and shellac, but I will make sure that the wet epoxy doesn't come into contact with dry shellac.