I'm may be being a little hypocritical here. I have a glossy white 12" ceramic basement floor left by the previous owner. It's pretty basic, but very easy to keep clean. Ceramic and especially porcelain are very effective vapor barrier, but they won't stop flooding, naturally. They are however cold to walk on. I've been analyzing a basement reno and am tempted by some of the solid vinyl flooring systems that can lay right over. I found some stuff that is a dense solid vinyl all the way through and is just 7mm think. It's molded, not printed, with a grain pattern out of solid color that runs all the way through the tile. It's even convincing to the touch. Someone I know laid it over her basement tiles and it looks good. Her installer said there was no need to fill the grout lines because the material is very dense and will not "sink". I'm not so sure. I want to wait a few years and see if the grid pattern from her tiles shows through.
I feel like it's a little different if you're floating a floor over something bonded to a slab on or below grade, but perhaps I should heed my own advice, or at the very least spend the time filling the grout lines with synthetic self-leveling compound?
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