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Bob as for applying extra coat .
there really is no set answer for that .
so people say they start with sanding grits like 800 then keep braking the grits down untill they get so grits like 3000 .
if your doing that you will need at the least 3 extra coats or by the time your finished wet sanding and then buffing you would not have anough mills of top coat on the car to protect the substraights .
then there is the simple truth about if your having to start with a grit that course
(of say 800 ) then you may as well just repaint the car because if the finish is that bad you ****ed up some were to make it that bad . or because you had to put so many extra coats of paint on because you were planing on starting with 800 grit to star you wet sanding i. the finish will be so orange peally for that amount of top coat you would have to start sanding with 800 just to knock the peal down .
when it comes to painting the rule is coverage plus one coat . so if your covered in 2 coats then apply one more . you should only have to color sand with say a 1500 or 2000 grit . any compound will take out that sanding grit scratch with ease . as most compounds are = to 2000 grit . and yes most compounds have cutting grits to them . to see just put a little between your fingers and rub them together . kind of gritty right !
so even to color sand with a 3000 grit is kind of point less as your compound has more cut to it than what you sand with . were the ultra fine grits come into play is on things like you have a stain from say bird crap on your hood with a OE finish . you tryed to just buff it and it's still there . you have to give it a little wet sanding but if you sand it with some thing like 2000 you could sand and buff right thru the OE finish because the does not have the mill build as what a repaint would have . a oe finish at most will have 1 to 1.3 mills of clear were a repaint will have 2 to 2.8 mills of clear . so you would want to use a 3000 grit on a OE top coat and a compound with little to no grit to it . again it comes back to trying to leave the most clear or top coat on the substraight as you can to protect it .
also the more product you spray on a car the more waves you put in the finish . the same holds true for sanding . yes you block your work and primers to get them as straight as you can but once you get them straight you want to leave it . you don't do your straighting or fixing with top coats . you want them to be there best and try to leave them there best .
so this comes right back to the begaining . you want to have your body work and primer smooth and straight . you want to lay down your top coats like glass the right way the 1st time then you only should need to do very little color sanding and buffing with just one or two sanding grits of 1500 and or 2000 . that's it !
all the crap you hear about people adding clear to the last coat of the single stage and crap like they spray the car then sand it and repaint it or they spray 6 to 8 coats of clear or top coats on is them just telling you they have no idea of what they are doing .
top coats are NOT like penuses more is not better .
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