Remove nitro laquer
 

I am about to purchase a guitar but the back has some laquer issues. It is nitrocellulose laquer and i want to french polish the back and sides. What is the safest way to remove the laquer? .

Nitro is evaporative, so adding additional nitro thinned with lacquer thinner will melt into the existing finish. That would avoid removing the existing finish and perhaps simplify the process.

What kind of instrument are you working on? Why FP rather than lacquer?

I will work on a Avalon L2-20... the back has some issues in the laquer from the builder. I can get this one cheaper so worth the fix. Frensh polish i like to use this technique on this great guitar. To see how it sounds after aplying it.
So thinner should do the job. I dont want to sand it of to prevent me to sand down areas more then other.

Lacquer thinner will dissolve lacquer, but be aware if the guitar has plastic binding, it may soften that as well.

Isn't French polish supposed to be applied to bare wood ?
There should be a sealer applied under the nitro and over the pore filler . The shellac in French polish may not be compatible with that sealer and you may need to sand in order to have proper adhesion .

Otter's right about FP going on bare wood, if you intend to refinish the entire guitar. Most chemical strippers work on nitro and take off most of the finish, but you will still need to get the remainder off with lacquer thinner or acetone. That will probably remove most of the pore filler, which will be replaced in the FP process. If there's plastic bindings, they will need to be protected or replaced.

Repairing the nitro would be much easier, unless you are already adept at FP. Even then, getting all the old finish off would be a lot of work with some pretty nasty stuff.

Ok thanks , i will post a picture of the back as soon as i have it. There are kind of bubbles between 2 layers as it looks like. I am aware that i need to go to the bare wood and start the process. But maybe when i can post a picture you have the golden tip for me.

Actually, to repair, you can use lacquer thinner or cellosolve to amalgamate the finish on the back and add more finish afterwards. Most lacquer is sprayed but it can be brushed if you’re careful, and it will keep the finish original-ish.

You can French polish on top of lacquer (or most any finish), but in this case, the delamination needs to be addressed first. Lacquer retarder will readhere the lacquer. After that, I would sand it down (not to the bare wood, but close), then overspray with lacquer or apply French polish.
IMHO, going to the bare wood is not necessary, and IMHO efforts to make a back finish extra-thin will not be noticed in the sound. Top finish is a different story.

I have a mid 70s, 335 gibson in today for a top refinish. IMO, the best and safest way to remove finish is to get yourself comfortable and simply sand the finish off by hand.

It’s a slow process but yields the best results

Steve

Thanks all for your kind reply, i think i will sand it down and start from there. I use to remove laquer with a piece of glass but on my guitar i dont dare to do this.