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.

wet sand until its smooth. feels almost like plastic when its smooth

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.

I did guidecoating on my prior applications of primer. I used the 3M dry powder guide. Really showed up the dips. I think it is now flat, so I wasn't planning on using a painted guided coat on the final sand, unless you think it is necessary.

I did guidecoating on my prior applications of primer. I used the 3M dry powder guide. Really showed up the dips. I think it is now flat, so I wasn't planning on using a painted guided coat on the final sand, unless you think it is necessary.

I would use it every time you sand primer. It will show you when you have sanded enough to remove the 320 grit scratches. I have had mixed results with the 3M dry guidecoat when wetsanding. It seems like it washes out sometimes causing you to quit sanding too soon.
I use SEM aerosol guidecoat.

Just before we put on basecoat or sealer if we use it, we use 600 wet

if you finish with 600 on urethane primer and there are no burn thrus go right into base, sealer only adds to the orange peel and dust, if you have g\burn thrus either reprime spot or plan on using sealer

if you finish with 600 on urethane primer and there are no burn thrus go right into base, sealer only adds to the orange peel and dust, if you have g\burn thrus either reprime spot or plan on using sealer


If your sealer isn't laying out flat you need a better gun or technique.
This is why I don't like low price topcoat guns, inferior atomization = orange peel.
600 unsealed can be a little coarse for some metalics and pearls.

thanks but i did not say i had problems with orange peel, i SAID it can add to the orange peel, and last time i checked, my sata nr2000 1.3 and my iwata w400 lay anything it sprays just fine.
600 is fine on 99% of colors, a few dodge colors and chevys pewter can cause problems(CAN) not always, if i think there may be a problem i will apply one coat of colorless basecoat.

I agree with Jake. Non sanding sealers may be fine for most driver quality cars, but sealers will add texture that will show in the base coat under careful inspection, especially in metalics. No sealer sprays as smooth as a 600 grit sanded surface, no matter what brand sealer, what gun, or what operator. We aviod sealers, we do exactly as jake recomended, spot prime and be sure it is all sanded slick to be sure the reflection of the base is clear.