Stripping an acoustic back to bare wood

Flip

My wife is an artist who uses guitars I build or renovate as her 'canvas'. She uses acrylic paint. On one previous occasion, I successfully stripped the soundboard of a used guitar back to naked wood using a sander and hand rubbing. That worked well.

However, I purchased a used dreadnought-shaped instrument the other day that has a light gloss varnish on the soundboard but a dark brown finish over the headstock, neck, heel, body sides and back. In a couple of places on the neck, the dark brown has been damaged which allows me to see that the finish has a significant depth above the wood - a bit like a coating. My guess is that this is, or is likely to be, nitro.

Would you confirm my guess or could it be poly?

In either case, it has to come off. Is the best way to strip off the dark brown using a chemical stripper or is another method preferred eg heat?

I plan to oil the neck and colour spray can prepare the body, the sides and the headstock and finally finish my wife's artwork with several coats of clear coat gloss. 

ICBM

If it has significant thickness, is hard and 'glassy', and especially if the guitar is relatively cheap and made in the far east, it's very likely that the finish is polyester. (Not "poly" .) It's almost certainly not nitro, which is usually very thin.

The bad news is that if it's polyester, solvents or even stripper probably won't touch it. You will need heat - quite a lot of it, which is a problem if there's plastic binding - or to simply sand it off, which will be a huge amount of hard work.

In the less likely event that it's polyurethane, stripper might get it off. Probably worth a try first.

more

You can test with solvents to establish what the finish is .French polish can be removed with methylated spirits and wire wool. You can remove cellulose with acetone. Poly is harder to remove and needs to be broken down with  a paint stripper  . I prefer to sand off ,poly finish .The chemicals in pant remover can stain the wood . You should wash it off with a lot water ,I don’t like using heat, you are taking a risk of doing some damage to the wood. If your repainting , you don't need to strip it to the wood . Rub it down and use a good primer.

DartmoorHedgehog

I took the finish off an '80s Hondo 12-string by sanding. I chickened out of using heat because I was worried about the glue giving way (the fretboard had previously come off pretty easily using an iron and hot knife).  It did take quite some time to do - the easy bits I did with a little "mouse" type power sander, but a fair bit of it had to be done by hand.

One thing worth mentioning from my experience is that, on my guitar at least, the nice-looking top layer on the laminated sides is VERY thin and I did rub through it in a couple of places before I noticed - doesn't affect the way it plays of course but doesn't look that pretty.  If you're planning on painting over it anyway then it doesn't matter so much.

Flip

Once again I am awed by the knowledge and generosity here, thanks everyone.

The two small damaged places on the neck will lend themselves to a superglue repair so I'll leave them until I find out how hard it'll be to remove the stuff on the neck. It is a cheapo instrument with the label removed (in shame?!) so I'm assuming since it's all the same colour apart from the fretboard and the soundboard it'll all be the same stuff.

Thanks too for correcting me re polyester and polyurethane. The clarification means it's almost certainly polyester. Given the advice received here, I think my good lady, she who'll do the art decoration, will be persuaded to leave the dark brown stuff as is and to concentrate on the soundboard that I'm fairly confident will allow itself to be machine-, then hand-sanded. 

Thanks again.

andy_k

Does it have to be stripped back to bare wood?, a good going over with 120 grit would be a perfect key for any type of paint, assuming it is the typical poly we are all used to on cheap guitars.
Stripping finish on cheap instruments usually leads to disappointment, in my experience, a lot of hard work to find a veneer or plywood, better left covered up.
I'm sure it depends on the finished art we are discussing, but getting the finish off these types of instrument is a daunting task. 

Flip

This seems to be a solution with broad support. Thanks to everyone.