Airbrushing a car, help please.



Sorry for asking a question that has no doubt been asked before.
My lack of search skills and patience got the better of me.

My neighbour has asked if I would like to paint something on the side of his old VW Kombi that he is restoring.
Anyway, I have never airbrushed on anything other than papers and woods. I've only ever used water based paints as well.

I was wondering if someone could be kind enough to point me in the right direction on how to prepare the surface, materials to use etc… Any guide on automotive painting would be awesome!
It's not going to be a show car, but I would like to do a decent job.

Thanks :)
First you will want to clean the existing paint, then scuff or sand the surface well, tack rag, clean again, tack rag again, now you can paint. Paint can be water based, like wicked or Auto Air or ETac private stock any lightfast paint. First start with a sealer if the paint has one, Auto Air does, this will help with paint adhesion. Otherwise paint right over the car's paint . Then you will want to clear it with automotive grade urethane clear for best durability. It is a good idea to find out what type of paint/clear is already on the car. It is is a lacquer based system, might be better to clear the art with lacquer rather than urethane, this will help eliminate any possible issues.

Now if I screwed you up, hopefully someone will chime in and straighten me out.
And do a test panel first, airbrushing on a non porous surface is way different, requires different reduction and pressure.
Wayne has given some good advice - if you are only painting a picture on top of the body work then I would suggest an 800 grit water paper to scuff it up, maybe even a 600. if you are base coating it then definitely a 600 grit. I have seen people using the 3m scuffing pad too. I managed to pick up a Harley mud guard from the agents by asking nicely for any insurance rebuilds were the insurance company hadn't collected the damaged goods that were replaced. I have been practicing on that. I was also advised strongly by a vehicle repair shop to use the best type of 2k clear.
And do a test panel first, airbrushing on a non porous surface is way different, requires different reduction and pressure.

As just me said here, it's important to remember the main difference between paper and any non porous substrate is there is a much higher risk of spidering, so will have to adjust pressure, thinning of your paint and your normal working method to accommodate this, other than that the rest has been said.

So like Justme said, a test panel is always a good idea, maybe you can find and old metal panel that is finished and have play around on it, this way you get an idea of what you can expect and avoid nasty surprises when you get onto the real thing.
Besides the differences in prep and paint just treat it like you would smooth paper or smooth clayboard/canvas..It will take you no doubt a little bit to get used to spraying the new paints (Most find them easier as they generally spray very smooth) but ultimately the main difference is size..It just takes longer but most techniques are pretty much the same..You cld practice on an old computer case or something, will help with basic prep also, but if your spraying over something he has restored it shld have a nice base coat to work of and will likely only need a light rub to get good adhesion...My main advice would be to find out what type of paint he has based in and continue with the same or similar types..Good luck with it..
I forgot to mention that before you even start to prep the car, it is important that you clean the surface with a good wax and grease remover. Otherwise the wax that is present on most cars will get into your sand scratches and can create adhesion issues later on.