Hello,

Is it fine to sand and paint primer over iron filings that are etched into my plastic bumpers?

I just washed the bumper cover to my 1990 BMW 325i with Stoner's Tarminator, Meguiars Super Degreaser, Palmolive original dishwashing soap and wanted to make sure that I don't sand the filings in deeper or anything. Of course before I start sanding I plan on using my PPG wax and grease remover.

What grit does autobody101 recommend I scuff the existing paint with before I put on my rattle can SEM flexible primer surfacer?

SEM didn't note anything about grit in the technical data sheet so I wanted to make sure the primer bonds well to my bumper cover.

1. sand the defects out of the bumper. You won't drive them in deeper, they are most likely superficial.

2. 320 grit would be fine, or a maroon 3M Scotch pad 7447 or equivalent. Or a grey pad with scuffing paste. The tech sheet does describe this: http://www.semproducts.com/wp-content/u ... rfacer.pdf

Also a toll-free number in that tech sheet so you can call SEM to make sure whatever you are painting the bumper with will play nice with that 1K aerosol primer.

3. Don't yell, we can hear you