
Re: Very rusty '86 Bleu Celeste.
1200 is too fine for primer 'cause you still want some tooth left for the topcoat to grip on to. For solid colour 600 - 800 is enough. Did you spray a guide coat?
Keep the primer layer thin but smooth, and remember that the cellulose paint won't 'fill' any scratches or marks like 2k will, so if you do have any in the primer use a stopper to fill them then flat it back again.
The number of coats depends on yourself and how you apply them. It also depends on the colour (yellow for example needs more coats) and whether or not you are going for a finish that can be 'rubbed out' with wet flatting and Farecla or not.
If you've never sprayed before then putting on enough paint to be rubbed out afterwards is a good idea as that gets out any final blemishes.
What I did was:
Primer:3 coats of primer, rubbing it almost off again between each coat to get the surface really smooth. Any tiny holes or pits need to be stoppered then and made flat. As mentioned where I did leave the primer thick the paint chips off easily.
Colour: 1 'mist coat', quickly followed by 3 full coats of cellulose top coat mixed 50/50 with thinners. The thin mist or 'grip' coat helps to stop runs by going tacky and gripping the subsequent full coat. The full coats can then be applied within 20 mins of each other, just leave enough time for the thinners to flash off properly. (15-20 min each coat @ 20c depending on temp.)
Let it dry over night.
Next, lightly wet flat the paint with 1200 paper and warm slightly soapy water to remove any nibs (bits of dust) or orange peel etc that might be there in the surface. This part feels awkward, especially if you think the paint looks 'good enough' already, as taking wet and dry to it just feels plain wrong...but trust me.
Rinse and dry the surface then look along the paint where you have flatted it to make sure it is all uniformly dull again, any shiny bits are where you have missed so you need to get them.
Degrease with panel wipe, tack the surface with a tack rag and you're ready for the next coats. This time mix your paint either 60/40 or 70/30, the larger number being thinners. The reason for this is that the thinners make the paint flow out better, giving a smoother surface straight from the gun. The downside is that with thinner paint it's easier to get runs so keep your gun hand moving! Another three full coats should do it, it sounds a lot but celly is really thin stuff.
Once that is dry you can appraise where you're up to. You should by now have a good even coverage that is quite glossy, but not super glossy. If you have any runs or orange peel then you need to let them dry thoroughly before flatting them back out, if not, then you can now decide if you are happy to go for the finish or not. If not just repeat the previous step until all is well.
To finish, you can either flat out the paint again with 1500 - 2000 before buffing with Farecla G3 which will give you a 'mirror' finish, or simply rub it out by hand with Farecla G3 on a damp cloth without the additional wet flatting. I'd advise the latter, as a mirror finish shows every little imperfection so can actually be counter productive.