Just thought I'd share a recent experience with y'all...
Some of you probably remember the 2 or 3 related posts I made a few weeks back, asking advice on prepping & refinishing Cultured Marble (which is basically a glorified plastic).
Here's how it came out:
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Here's how I did it, step-by-step:
1. Disassemble any and all hardware that penetrates the Cultured Marble surface (faucets, etc).
2. Clean surfaces EXTREMELY WELL.
3. Scuff sand every inch of cultured marble surface. I found a 1/4-sheet finishing sander was quite helpful in this step. Make sure no gloss remains - but don't sand too deep, or you'll create more imperfections to fill in the next step.

NOTE: you might want to mask for the dust this will create, especially if you have to sand off a previously-applied coating.
4. Fill any imperfections in the surface & sand the filler smooth. I used the polyester-based bondo with great success(grey with white hardener cream).
5. Mask for spraying.
6. SPRAY bonding primer (XIM recommended, I used the UMA water-based) with an HVLP rig.
7. Lightly sand primer. (no power sanding here!)
8. SPRAY your finish coating of choice. I used Fuhr 260 Aluminum Oxide Modified Urethane - Waterborne; I chose this coating due to deep tone color needed, and excellent water/chemical resistance properties. Note this finish needs to be sprayed on in THIN, multiple coats (especially with a deep tint).
9. Depending on coating chosen, you may want to lightly sand (by hand) between finish coats. (I did, as my test boards showed this particular coating wanted to "rope" if applied on a smooth, non-sanded coating.)
I strongly recommend avoiding any non-spray application techniques on Cultured Marble... for some reason, this kind of surface seems to hinder the self-leveling properties of the coating when brushed, rolled, or padded. However, when sprayed, the coatings self-level beautifully. This applies to both the primer and the finish coats.
This kind of project can really save a ton of $$ for the homeowner, as in this case the demo & rebuild of the shower walls alone was quoted at over $2000 - and that was before they considered replacing the tub *or* the sinks & countertop... So, instead of dropping a few grand on replacement of the countertop & shower, this homeowner decided to spend a whole lot less and refinish instead.