Rather obviously, to spray paint you need a spray gun and an air compressor. I took advice from a professional with regard to spray guns and was told buy any make you want as long as it's Devilbiss. Mine is an FLG5 purchased new on E-bay for about £70. Having used the mickey mouse cheapo ones from SIP, Sealey etc I can't stress enough how much a decent spray gun is essential.
I have a SIP compressor with 100 litre receiver rated at 15cfm, bought it years ago and despite the wheels dropping off it seems OK.
One item many home sprayers forget is a mask, my local paint suppliers recommended the disposable 3M type, less than £20 if I recall and mine's lasted over a year.
2. Paint
Preferences vary, but I've found Williamsons Transpeed about the best for home use. We use it on our buses and I gather trains are painted in it too. It has a high solids content so covers well, and is quite forgiving. I use Transpeed undercoat as well. It goes without saying that when ordering paint make sure you order the correct thinners to go with it.
People rant on about etch primer and aluminium, I don't bother. I've used Rustoleum Galvinoleum 3202 for a long time, on both aluminium and galvanised steel. So far nothing I've painted has peeled off, and I started using it 7 years ago. It's a bit wierd to say the least, but sticks to anything.
3. Other materials
1.) Panel wipe, or body clean. A solvent that when wiped on material to be sprayed removes any trace of grease
2.) Tack rag. A sticky cloth that removes all traces of dust and particulates from the material to be sprayed.
3.) Masking tape. Do NOT buy this from your local DIY superstore as it's crap and not suited for bodywork. You'll find that it's not only vastly superior, but cheaper from your local paint supplier as well.
4.) Masking paper. Cheap as chips roll of brown paper for masking.
5.) Gunwash. A rather evil solvent that dissolves most paints. Cheap, so better suited to cleaning equipment with than the paint thinners themselves, about £7 for 5 litres.
6.) Vast quantities of paper towel!
4. Preparation
In my experience there's only one way to go. Bare metal everything. Takes time, but it's worth it in the long run. Nitromors and wire wool is best for not too many previous paint layers, for ex-MOD vehicles I'd use a D/A sander and 180 grit discs to remove the worst or you'll need a mortgage for the Nitromors. When buying an electric or air D/A sander always go for one with a 150mm base plate, as this is pro size and sanding discs can be had from as little as £20 for 100. The home 125mm discs are frighteningly expensive in comparison.
It took me roughly 2 hours to bare metal both these hardtop side panels, but they only had one coat of paint on top of the factory layer.
Once bare metalled and washed off, mask the relevant areas, clean with panel wipe and rub over with a tack rag.
5. Priming
Thin the Rustoleum 3202 as directed and blow over. Don't worry if it's not totally even, as long as everything is covered.
6. Undercoating
This can be carried out immediately, as by the time you'll have cleaned the gun the Rustoleum 3202 will have dried.
Thin the undercoat as directed, and don't be afraid to experiment. As the day I sprayed these panels was warm, I only added about 25% thinners and sprayed on two coats leaving a few minutes between them.
7. Top coating
OK, so you've been a bit hit and miss with the undercoat and got a nice even covering and are now getting over-confident, this spraying lark is easy.
STOP
The top coat has far less pigment in it and a much greater tendency to run.
I let the undercoat dry for about 15 minutes (it was touch dry by then) and then sprayed on two top coats, leaving about 10 minutes between them. Thin and even is the key. But not so thin there is not enough paint to level or the finish will be like sandpaper, and not so thick it runs. With practice it's not too hard. Don't be fooled into trying to get the top coat to cover in one application, chances are unless you get it spot on it will run.
8. De-masking
Once the paint has dried, after about 2 hours, I remove the masking tape. As the paint is not hard be careful, but the benefit is any overspray can be carefully cleaned off with thinners before it is totally set.
So, there you have it. The way I spray. Probably totally wrong but it works for me, and gives results a zillion times better than a brush IMHO.