what grit are people sanding there car back with before highbuild primer... iv read that 80 grit can shrink over time, would 120-180 be better I don't want to go too fine as I want the primer to stick.

 

There is a spec sheet with the primer that guidlines the required prep.....but finishing over filler..... 180- 220 grit or there abouts, feather edging with 320 was on a "evercoat" polyester high-build primer line I looked at for example.

 

I work at a body shop, and we use 320 or 400 grit depending on the type of paint we use

 

so scuff paint back with 320-400 then apply high fill primer??
could I go courser if I wanted to or will it risk shrinking back into the scratches?

 

You could go more course, but you might see sand scratches, put 3 coats of primer, then block it with 400

 

i have to take off a few layers of paint back to the factory paint job so i might hit it with some 120 as the 180 grit clogs too fast. then put 3 coats of the high fill primer let it sit for a few days to let it shrink or i might spray it in a booth and bake it, then guide coat it and sand with 400 and see how it comes up. would it be alright to re-prime over 400 if i can still see the 120 grit scratches??

 

Yes it will, it will also give you a chance to get it perfectly straight if you missed any spots

 

no worries that's the way ill do it I reckon,
sand the body till im happy with 120 repair any rust/low spots that I find,
then apply the high fill let it cure/shrink,
guide coat then block back with 400,
ill most likely be choosing a solid colour so no need to sand any finer and hopefully my rx7 will be ready for paint.

another question..... would there be much adhesion difference for the primer between 120 and 400??
if my car just had the factory paint job then I probably would of just used the 320-400 before the primer would make things a lot easier.

and thanks for the advice bro.

 

It will stick no problem