which grit and block on primer

[KevinR]

I am making my first attempt at body work and have a few questions. The portions being worked on are in sandable primer and I would like to know what grit paper should I start and finish with. can I do this with my hand, a DA or on a sanding block? Do I remove as much primer as I can like a final top coat of filler or do I want the panel to all be the color of the primer with no sand through's?

You help is appreciated
Kevin R

[28bmod]

Spray Some Flat Black Spray Bomb On The Primer Just Light Enough To Verly Cover It - This Is Called A Guide Coat Use A Short Rubber Block With 220 Grit If You Cut Through The Primer Dont Worry Just Respray The Spots . Do One Panel At A Time And Watch Out That The Rubber Block Does Not Dig In Keep If Flat If You Are On A Rounder Surface Get A Piece Of Pcv Pipe To Use For A Block . With The Guide Coat You Will Be Able To See All The Scratches In The Body Filler And Low Spots . When This Is Done Use 600 Grit Wet Or Dry And Use It Wet And Use The Block On All The Big Flat Surfaces And Seal And Paint

[CARS]

since it is in primer I assume it is straight already and you are just getting rid of the scratches.
Always use the longest block you can. On a hood I use a 30" long block, for things like cowls and rear window fillers I use a short one. Longer means no waves.
For sandpaper I start with 180 and completely sand everything. Clean it up and give it a couple more coats of urethane primer (2K). Then I sand that with 220 and finally 400 grit dry, blow it off and wet sand with 600.
If you go through anywhere but you don't need anymore primer to make it smooth you will have to apply a primer-sealer to the bare metal areas. Top coats do not bond very well to bare metal so don't skip this step unless the bare area is just a edge or something the size of a dime.

A couple tips: Using the mentioned guide coat is a great idea. Use the same paint company's primer as you have top coats. Don't use primer as a body filler, it is for scratches (slick sand is pretty darn thick though). Thick primer coats may shrink a couple months after you are done painting and cause the scratches to reapper. Light but wet coats with the proper flash time between is the key.

Hope this helps. Good luck