What grit sandpaper should i use before primer?

[ricklovin93]

title says it all, finaly got the ambition to get this fender replaced, what grit sandpaper should i use before primer, i used 120 grit to take most of the visible paint off, what should i use for the inside of the fender? I was thinking like a rubber undercoating or something to try to protect it from moisture

[94 olds vert]

I'm a little confused. I would sand with 320 before primer. The inside you never see anyways. I've heard that rubber undercoating isn't that good and I'd stay away from it.

 

You could paint the inside of the fender with a primer that inhibits the growth of rust.

[RobertISaar]

most primer doesn't actually seal out moisture, so if you prime, you might as well paint it.

 

however, when it comes to rubberized undercoating, it works.... if you spray it on a painted or otherwise finished surface. my dad had it sprayed on the bottomside of his 70MC, had it cleaned up beforehand, but no paint. after a few years, it was all flaking off with significant amounts of rust popping off with it. this car had never seen winter/salt in his ownership.

[ricklovin93]

So your saying sand with 320 grit before priming, because right now it's sanded with 120 grit and is pretty rough.

[94 olds vert]

So your saying sand with 320 grit before priming, because right now it's sanded with 120 grit and is pretty rough.

 

Yeah if it's too rough you will have scratches in your primer and that will show in your final coat. The more you work them out the better.

[sl3196]

Ya I wetsanded the lebaron with 320 before primer and paint.

[rich_e777]

I thought about using a spray on bed liner to do the undercoating if my rust gets to bad. Not much yet just a little here and there. Probably work a little as soundproofing too.

Edited April 10, 2012 by rich_e777