Hello guys, I am new around here. I'll share my experience on DIY paint job that me & my brother (He did the most of it) did for the Maruti 800 we owned.
We painted the whole car once in solid white. We used 1K paint single stage solid white paint to do the job (Yes, you could put new paint over the existing paint and even a slightly different color too). It was bit of an experiment which the results turned out to be quite good (Didn't get the factory finish but it was acceptable). I'll write down some important points we noted during our experiment and how we carried out some of the tasks.
Paint Gun
You should find a decent paint gun to do the job. You could mange with a Chinese paint guns which costs 1k-2k but they are bit unpredictable unless you are used to it. But our experiment was done with such a gun that 1.2mm nozzle (Few year later we got hold of "Ingco" brand paint gun (1.8mm nozzle) which turned out to be quite good too. But it's expensive).
You should first take a metal panel (a wall or wood panel won't do because they are more absorbent than metal) and try the gun yourself. Paint guns usually have valves to adjust air flow and paint flow. And there is another adjustments for spread area. You should get familiar with these adjustments so you could get desired outcome.
The distance from the gun to paint surface is also very important. If you get it too close your paint will start to drip. If it's too far the sprayed paint will turn into dried dust and deposit on the surface. The optimum distance changes with the gun and its adjustments.
Painting surface
Our subject had a solid white paint without a clear coat. So we sanded it using 600 grit sand paper to make the surface rough enough for the paint to stick properly. As far as I know clear coats should be removed completely. We used wooden & rubber blocks when sanding to avoid getting uneven surface.
Painting area should be made absolutely even (We did as far as we can). And it should be free from oil, grease or other contaminants which affect the paints ability to stick to the surface.
Repairing dents
When repairing minor dents we removed the paint layer also but didn't go down to bare metal since the OEM primer seemed to be quite sturdier than the ones we could find in the market for the price we looked for.
We used metal filler (cataloy, apploy etc...) to fill the dent and sand ed it down when it's hardened. We repeated the steps until we get a very fine surface over the dented area. Then we used a primer over the area.
Removing Rust
Removing rust was a tricky business. We tried to sand it down but sometimes it was not possible because of the uneven surface. In those case we used Phosphoric acid. It could dissolve rust faster. It does react with the metal too but at very slow rate. We used a tooth brush and this acid to remove rust in the places where it's difficult to sand.
It doesn't burn our skin but better to you gloves when handling it.
Paints & Primers.
Stick to one brand of paint and primers. Don't mix different brand because sometimes because of incompatibilities of the paints they start different chemical reactions. The paint may start to bubble up after you sprayed it. It happened to us once.
You could have an idea of the terminologies like 1K paint, 2K paint etc... from here http://www.eastwood.com/1k-coating-vs-2k-coatings
As far as I know 2K paints are bit toxic than 1K paints. Please correct me if I am wrong.
Place to the job
In our case we used our garage in front of our house. It's surrounded by 4 feet walls int two sides, one side by the house and the other by the gate. We used polythene to cover the gaps from the walls to the roof so floating dust could be avoided. We also fixed a blower fan to suck the paint fumes out of the enclosure. This was quite sufficient for what we did.
Weather
We selected dry days to do the painting. Don't spray paints early in the morning and very late in the afternoon. Since it's bit cold during these times of the day the paint gun tend to accumulate water inside it unless you have a water filter fixed to the air hose of the gun.
And don't spray paint when the paint surface is cold. It could happen in early mornings.
Safety
Please use a mask to cover your nose and mouth. You could buy one from a shop which sells safety equipment. Also wear a safety glass.
This write up is entirely based on our experience and some information found in the internet. So don't expect it to be professional advice. I hope it might help you out. You could find lots of Youtube videos on this subject which are very helpful.
