Proper way to sand plastic before painting?

Seems to me that you're doing it just fine. The problem may lie with the fact that you are not priming the plastic before painting.

Try using a model primer or, as I do, a thin spray of cellulose car primer.

i use the disposable nail buffers to remove that. find a 4 way and use the shine edge. at your cosmetics counter.

Primer. Thou must prime before painting. Not only for its paint adherance but the primer will also help to reveal flaws in the prepared surface that might require further attention with the sandpaper or filler before you lay on your topcoat(s).

WmB

First, one basic question: WHAT are you sanding?

You mention "fuzz", which is typical of sanding vinyl kits. I don't know how builders deal with that problem.

Resin can also be problematic. Often the surface of resin parts is hard and smooth while the interior can be softer and appear porous. In such cases, a thin coat of superglue, sanded and polished, can re-seal the surface.

If you are sanding styrene, 600 grit should be just fine - especially if you are using matte paints. Gloss and silver may require higher grits depending on your painting technique.

I suspect the problem is with the "washing" step. You need to remove not just the sanding dust, but also the mold release and finger oil. Hot water and detergent (not soap) followed by a nice alcohol wipe works well. An old toothbrush, toothpicks and cropped acid brushes are very helpful in scrubbing all the debris out of the nooks and crannies.

And yes, a primer coat is always an excellent idea. Find the boo-boos BEFORE you get serious.

Greg Reynolds, IPMS

I'm sanding styrene. I used hot water with detergent, but I just wiped it. I should probably have used a toothbrush.

Yeah, as others have mentioned, I will use a primer for the more important parts of the kit (the Academy 1:48th CH-53E, incase anyone was wondering).

I assume a flat, light or medium gray Tamiya acyrlic is OK as a primer?

Thanks, Just> First, one basic question: WHAT are you sanding?

Only on crappy resin kits, properly done resin is monolithic.

Detergent and alcohol do not work well enough on some of the resins now being used (Smooth-On resins in particular, usually white or grey in color). A detergent and toothbrush wash is a good idea to get particulates off the surface but you need a silicone stripper like Westley's Blechewhite tire cleaner to really get rid of the mold release.

I usually prime surfaces before painting. I use Krylon sandable primer. I learned to use it a number of years ago based on recommendations from this list, and use it exclusively now, though I am sure there are other primers that are good.

Also, did you wash with soap and water, or just water. If you used soap, you MUST rinse thoroughly to remove any trace of soap/detergent film.