What grit sandpaper should you use to take down body filler and or primer?

Usually you would use a progression of grits. For plastic body filler rough shaping you might use as coarse as 36 grit on an air-file, then smooth with 80 grit and finish with 220. Many techs skip the 220 for filler, but it means you will have to fill the sandscratches with putty after priming the first coat. For primer wet-sand with 220 wet-or-dry for the first coat or two, then 400, then 600. Tip: after you are finished sanding the filler, if you have time, let it sit for several hours. The filler shrinks a little during that time. If you prime and sand right away, the repair will sometimes telegraph through and be visible in the finished paint. If you allow it to do all the shrinking first, then the coats of primer will fill the shrinkage and do a much better job of hiding the repair. I have had jobs come back because the filler shrank AFTER I finished priming and sanding. Not pretty. POLYESTER PRIMER IS THE BEST.........so if your using going to use polysester primer then : start with 40 then 80 and that's it..........POLYESTER PRIMER WILL HIDE 80 GRIT SCRATCHES............ if you still want to sand your filler more....but dont want to take it down to much further....or you just want to fill some deeper scratches.....then palm sand with 120 and prime. BUT...... If you are going to use any other kind of primer over your filler.......you have to use more grits PERIOD...... ANY OR ALL OF THESE: 40 80 100 120 150 180 220