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Problem

What grit for plastic bumper before primer?

Primer may not stick well to a plastic bumper if the surface is glossy or scratched too deeply.

plastic paint primer wet sanding
Answer

For a plastic bumper before primer, use 400 or 600. Use 320 only on rough repair spots.

Why it happens
Plastic bumper covers need a clean, evenly scuffed surface without deep coarse scratches.
Recommended grit
Use 400 or 600 before primer. Use 320 only for rough repair areas first.
Wet or dry
Dry for prep; wet can be used at 600 for finer cleaning.
Success check
The bumper surface is clean, dull, and evenly scuffed before primer.

What to do

  1. Clean the bumper surface.
  2. Use 320 only on rough repair spots.
  3. Scuff the full primer area with 400 or 600.
  4. Remove dust and residue before primer.
Avoid: Do not prime glossy plastic without scuff sanding.

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