Thanks for the replies fellas, as i said, im no sprayer but i'll give it a go and listen to any tips from more experienced sprayers.
Prep, prep and more prep. Cleanliness is paramount, even using for example silicone or Hylomar in the same area as the surface to be painted can cause fish-eyes so ensure you keep contaminants to a minimum, try not to stir up dust etc. When I am painting I sometimes lightly spray the floor with water to ensure that any dust stays put, it also stops over-spray adhering.
Get the vehicle (or panels you are doing at that point) fully prepped and cleaned, prior to painting clean it all again, even if it was only the 15 minutes you took to get the paint ready have the gun ready to go and quickly run over the whole lot with standard thinners, you can use pre-paint - I never use it - only downside to this is that if you run it over an acrylic primer or something it will lift the paint, but if your Defender simply has been rubbed down ready for primer then you will be fine.
Take your time, I had a friend who for years had had me believe he was a good painter, until one night we went to paint something, I didn't want to touch it, if anything went wrong then I would have wasted his paint so I let him do it. I handed him my best gun and he simply started to spray the panel, no test spray or pattern check, the nozzle was wound into a very narrow fan which was simply how I had assembled the gun, he hit the panel and immediately shot across the panel at about 100mph returning immediately and at a complete tangent to the previous pass, I just stood in horror. The result was something that resembled an underpass graffiti job!
Depending on what is to be painted will depend on the best gun setup but for a typical Landy panel I will screw the fan control out so that the fan is about 8-10 inches I would say. With something like a primer I tend to have the flow reasonable so that you get good coverage in a single pass, also most people turn the air volume up far too high, pressure can be regulated at your compressor but the volume can be controlled on the gun most people mix these up, if it is blasting heaps of air out and sending paint mist everywhere it is too high, wind it in until the paint just drips out the gun then start to give it some air and try that, then wind it up till you get a nice pattern and decent looking coverage. This sounds like a lot of faffing but once you understand the controls and the impact it has on the paint you will soon learn to setup the gun very quickly. I would even suggest getting half a litre of emulsion watered down a bit and try practise on the garage wall or something - just to learn how the guns behaves.
Paint viscosity can make a big different too, too thick and it will spit and splutter, too thin and it will heighten the risk of running back off the panel - however a good trick to get a very glossy finish is to load the paint up with thinners then hit it hard, works well on horizontal panels like the bonnet to get a really nice finish but that takes some practise. Another trick with metallic base-coats is to pull the gun right back and open up the fan on the final pass to get the metallics to stand up and give a more sparkly finish.
You can also make good use of the trigger control, you can alter the needle depth which will control the volume of paint, if you wind it right in you will only get a very small volume of paint delivered, I tend to set the gun about 50% on my gun which then lets me vary the fluid control with the trigger, when passing over a main panel area I will give it full trigger but say I am carefully coating a fuel filler recess or around a hinge or something I may make lots of very light passes when I just pull the trigger enough to get a very light mist of paint, but give it lots of them as hitting an angle at full flow will almost always result in a run.
Lighting, you need good lighting, you must be able to see the surface well so you can check obviously for coverage but more difficult to spot with poor lighting is orange peel, or a light coat leading to a rough finish, if you can see that well you can come back and add paint to fix it. I often will finish painting, disconnect the gun, lay it down and grab a high power lamp which I can shine over the job, if I spot anything I can grab the gun and load it up again, sometimes you end up needing to paint a whole panel again to get the finish right but concentrate on the iffy bit.
The first time I sprayed a vehicle panel I was given this advise, "Setup your gun with a some test sprays and put a pass across the top of the panel, then come back, overlapping slightly each time until the panel is done, just a very light pass so that the panel is really just misted with paint, step back for a minute and let the thinners flash off, now start at the top again and do 2 more light passes back to back, this should totally cover the panel and it should look good, let that flash off for 5 minutes then give it a final coat"
That is all I started with, I don't quite follow that advice every time now as over years of painting I have picked up a lot of experience, but that initial piece of advice stood me well and was good advice because it taught me to lay it on lightly and patiently. You can keep shooting more and more paint on if you follow that advice, just the little wait in between should, with a correctly mixed up paint, be enough to let it slightly firm up so the next coat won't cause it to run. If you get a run don't panic, there are options, if it is the lacquer then I would leave it and fix it once it had set.
Here is the best piece of advise I think I can offer you, don't panic, if it goes wrong, quickly asses the situation; a big mark where you accidentally slid the airline over the panel is probably ruined, but if it is just a small or even big run then the option of compounding the run out (assuming lacquer or top coat) will exist, if it is primer, who cares, you can sand it, base coat is different, you MIGHT be able to fix it but it would probably be better to stop. Let it dry, sand it back and start again. Always remember you can sand it off and do it again.
