Refinishing Nitro over Poly - questions

[Twigman]

I have a bright yellow precision that I built a few years ago.

It was a finished Warmoth body in Grafitti Yellow Poly.

I don't like the colour.

I am planning to refinish with black nitro over the yellow poly.

I plan to sand the yellow but not all the way off, perhaps with 400grit just to key the surface for the nitro paint.

Will this be enough or should I really strip all the yellow back to wood?

I don't really want to have to then fill and sand so would prefer just to leave the yellow on.

I plan to airbrush the black nitro on.

A couple of questions:

1  How dilute (xparts paint to xparts thinner) would be best?

2  What volume of paint is required to cover a precision body? Diluted or Undiluted?  - I ask this to establish whether my current (modelling) airbrush would have sufficient capacity in its resevoir without having to refill it too frequently.

 

I know these are proper newb questions but we all have to start somewhere.

Edited Thursday at 11:24 by Twigman

[fretmeister]

Strip it with a heat gun.

[BlueMoon]

11 hours ago, fretmeister said:

Strip it with a heat gun.

This ^^^^^^
 

………or first a binding coat of shellac over the prepared (sanded) poly. Nitro over shellac is fine.

 

Your modelling airbrush reservoir is likely too small. Repeatedly refilling it during the job could create issues that you don’t need.

 

Good luck.

[Manton Customs]

Nitro over poly is no problem and actually what a lot of the ‘nitro finishes’ are on mass produced basses. The primer/sealer coats are sprayed with polyester and the top coats nitro, this saves a lot of time as the poly has a  much higher solid content and will not shrink back/evaporate as nitro does. The same would be true for your bass…it’ll save a lot of time if you keep the old finish. The downside is it’s possible if you get a chip in your new finish, you may see the basses true colours at any damaged areas.

 

I would make sure you throughly scuff sand the existing finish, new paint may not stick properly to anywhere that doesn’t get abraded. It probably won’t lift and peel, but it will come away with only slight knocks/scrapes unless the surface is abraded. To ensure it’s got a really good scuffing I’d to go for 320 grit. You’ll likely see sanding scratches through this for the first couple of passes but you’ll be safe in the knowledge that you’ve got a good key. You also need to watch out for contamination from silicone/oils etc which could be on the existing finish. Wiping with acetone and/or lighter fluid is good. But silicone is pretty much impossible to remove as it just spreads.
 

In answer to your questions - there isn’t a one ratio fits all. You’ll need to thin it down to the point where you can get good atomisation with your air brush/setup. If you’re using a small airbrush setup you may need to thin considerably. It also depends on how thick the nitro you use is to begin with is. The stuff I buy is a sort of honey like viscosity and would be no good in an airbrush without lots of thinning. More thinning means more drying time between coats and a longer wait before final buffing.

 

The guys which use aerosols for this work will usually recommend a can of colour (400ml ish) for the colour coats. But it depends on your experience and again how thin the paint is. Always buy more than you need!

 

I’m not sure I’d want to do all the colour coats and clear coats with an airbrush. Though they can be a useful tool for spraying bursts and repairs. If possible you may just want to get an aerosol or two.