Question about which grade(s) of sand paper to use...

[jprastrullo]

when priming body parts? For example, I want to paint my side mirrors and trunk spoiler black (using SEM trim paint).

What is the general best practice for hitting body parts with sand paper before it sees any ounce of paint?

Conversely, I'm also looking to stripping/repainting my IS valance... Color is white... Any strategies on how I should tackle this? (for paint matching etc)

Anything will help :-)

[Rdreas]

when priming body parts? For example, I want to paint my side mirrors and trunk spoiler black (using SEM trim paint).

What is the general best practice for hitting body parts with sand paper before it sees any ounce of paint?

Conversely, I'm also looking to stripping/repainting my IS valance... Color is white... Any strategies on how I should tackle this? (for paint matching etc)

Anything will help :-)

If not using any filler and none should be needed the lowest grit you should go is probably in the 220 range. When prepping body work you generally finish for primer in the 180-220 range. When sanding primer you really don't wanna go below 400 but if you get a nasty run or something of that nature you can go to the 320 range.. but probably need to reprime after. Plastic parts you will want to use this method on and if there are any deep scratches you will want to use a 2-part glazing putty. It can be applied over paint but do yourself a favor and read the direction on the product here.
I would not waste any time sanding a valence I would jump straight to a spray on aircraft stripper. Make sure to do this outside and with a respirator (unless you like headaches).. spray it on wait a few minutes for the paint to bubble, scrape it off. Prime, block with 400, get a quality paint store to match your paint and paint and clear it.

[AndrewBird]

Aircraft stripper won't even touch the chip guard on the front valence. Use an angle grinder and a wire wheel. 100x easier and faster, though a bit messy and loud. Josh (Jan3rson) and I did his front valence this way. We tried aircraft stripper first and it didn't really do anything.