Dry sand using 180-grit sandpaper to remove rust or surface damage before moving on to a 320-grit paper to remove your previous 180-grit scratches. Whichever method that you decide, follow it up using 400- to 600-grit sandpaper to sand the paint to prep the existing paint surface for the new coatings to be applied.
Moreover, do I need to sand after priming?
Sanding after applying primer should help keep your surface as smooth and flat as possible, eliminating brush marks, or extra little globs. Also when painting, like others have pointed out, can raise little fibers from the drywall, going over the surface with a sheet of sandpaper can help get rid of those lose fibers.
| Grit | How It’s Used |
|---|---|
| 180 grit | A finer grit used to final sanding and feather edging body filler. |
| 320 grit | For final polishing sanding before the primer coat. Also good on spot putty. |
| 400 grit | Used for rough sanding primer. Also used for fine sanding spot putty. |
Keeping this in view, what sandpaper should I use on primer?
The goal of sanding wood that has primer on it is to smooth down the grain that has risen while still leaving the primer intact so you do not lose the added adhesion that the primer will provide for the top coat. To sand wood with primer on it you should consider a finer grit sandpaper (like a 220 grit sand paper).