I will be spraying urethane base clear system. Solid white in color. I read many threads and some say final sand is ok with 400 grit, some say 500 or 600. But should I sand the primer surfacer wet or dry.
I tried 400 dry but the paper seems to clog with dust quick. I am thinking maybe wet would be easier and get rid of the dust. But how do I tell when I wet sanded enough? Your experience is appriciated. My first paint.
PS I block sanded the surfacer and I think it is very flat. Used 320 grit on the last blocking and car now sits in uncut final primer coat.
Spray a light coat of black aerosol paint over the area. It's called guidecoating. It doesn't have to cover completely and make the whole surface black, it should be a mist coat. When you sand the low spots or scratches will be highlighted by the black. Sand until all the black is gone.
I know many people that sand dry. I prefer to sand wet. It cuts quicker and doesn't clog. Also if you wet sand and wash the sludge down the drain (legal in my area since it's dried paint) then you have eliminated alot of dust that could get in your lungs or paint job.
You can "get by" with 400 for a solid color if you use a sealer.
I prefer to sand with 600 wet. Since you've already hit it with 320, I would go on to 600.
You want to use guidecoat over primer and it will show any imperfections/low spots. SEM guidecoat works the best as it stays on the primer and won't wash off if you're wet sanding.
Here's picture of what guide coat should look like when applied properly over the panel
