hey guys... what grit sand paper should i use to sand my platic front bumber and ground effects when im repainting? and what is the process to do before primering?

 

220 Grit
sand everywhere you plan on spraying primer/paint
you dont have to sand down to the primer, you're basically "Scuffing it up" for lack of a better word so the primer will stick well and it is also getting rid of any small scratches, rock chips etc that may show up again when it is repainted. So if you come across any scratches/rock chips then make sure to make it smooth so you cant feel the scratch or rock chip because if you can feel it, you can see it. If it can't be sanded out use some body filler to level it out. Doesn't take too long.

Remember to be patient.

 

so the same goes for the plastic body peices? someone told me to use 600 grit for the plastic... then do what ever body fill s are needed and then primer... true?

 

I think 600 grit is way too fine for the job. I wouldn't use anything over 320 on those parts it wont make a bit of difference in the long run. Even for show quality.
On my own car im using 220 dry for the polyurethane/fiberglass parts aswell. There wont be anything that will show up from the 220 on the final paint.