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I tried my hand at French polish on my second build. It turned out pretty good for a first shot. I don't like the toughness of the finish. I would like to spray a couple of coats over top the shellac. What wisdom and experience can you share before I dive in. I'm a bit affraid of making a mess of things. Thanks for sharing.

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Mark Ewing
Columbus Ohio
"Trees are an important and precious thing. We should build good things with them. Building good guitars with heart are the best use for them." K. Yairi.

light scuff sand with 400 or 600 then spray your lacquer as normal. You should have no issues.

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

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I actually did this on a guitar some years ago. I chose to sand back to wood with 220 grit and start the Nitro process from scratch. My rationale was that I didn't want any of the oil that was used in the FP process to rise to the interface and compromise adhesion. Whether it would have will never be known but I took a far more conservative approach just to make sure I would be successful. After 4 years now, I don't regret the decision.

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

Nitro lacquer has been applied over a shellac sealer since its inception. Works great. Every nitro-finished instrument I ever built was shot over a shellac sealer. I've never even seen/held/hanlded vinyl sealer. I would also french polish(roughly) with pumice to pore fill under nitro. Just make sure to clear all oil off the surface, either through "spiriting off" or better yet, by wiping it with naphtha. Nitro burns into shellac, so you don't even need to sand it if it's oil and wax free.

What Grump said - Shellac is a great seal coat for nitro so you certainly don't have to sand it all off. Any oil that may be on or in the shellac should have been removed by spiriting off but if that step was not completely done you can still spirit off now prior to spraying nitro. Using naphtha is just another way to remove any oil residue too and could also be called spiriting off me thinks.

I have to send Grumpy an email - we compare pain in the winters by me telling him it's freezing here and he one-ups me and tells me it's a LOT colder where he lives - this is getting to be our winter tradition....