Transparent glass floors are usually large glass tiles (laminated and tempered) that are set into a metal grid. A silicon cushioning strip is set on the grid to cushion the glass. Depending on the system, the tiles are surrounded with a silicon strip built into the grid, or they are "grouted" with a silicon caulk. For large glass set directly onto a floor, it's usually set on a cushioning silicon mat. I suppose there are situations where a rigid bonding adhesive could be used (like a thinset) but the ones I've seen are flexible in nature. There's some really cool glass stuff going on out there. My wife and I were in a a bar in Barcelona that a lot of glass detailing: it had "lava lamp" type of flooring, bar countertop, and tables. Seemed to be two sheets of glass, gapped maybe 1/4" or so, with the liquid between the two sheets being just like a lava lamp. You press on the glass table or bar top, or press on the floor with foot pressure, and the liquid swirled around between the two sheets of glass. It was all backlit, very shimmery. Really cool. Not a good place to walk around when you're a little tipsy. They had glass stair treads which I thought were dangerous. We were there for a while and several people stumbled on the stairs. Didn't seem to be the alcohol. More of a depth perception problem.

Bill, thank you for your response. I'd always thought of caulk as not being much of a good fix for most things, because it never seems to hold up well or for long. Wouldn't this be the case here, or is tile different, or is there a special caulk used with tile that you're referring to that is more durable that that used between a tub and a tile wall? After thinking about this some more, it's clear that I need to consider Plan B and do the L configuration if it's to work at all because of the tile situation. So the next question is: --How far back would he likely have put the mud base? When we remodeled our old place, the mud went to the wall at the back of the vanity. --Is this what is normally done? If the tiler slapped down 12 x 12 sheets of the 2" tile, there probably is about 5" under the existing cabinet. If the mud base goes to the back of this vanity, that would give me another 13", giving me ~18" total depth, and I have enough leftover sheets of tile to cover this. --So if the mud base is there, shouldn't we be able to lay tile on it? --If the mud base is too rough, can it be either ground down in the high places or filled in with the setting compound? --How deep can the setting compound be and still do its job properly? Thanks for whatever clarity you can provide! Anne

Should I buy something to guard against moisture (ditra?) You can, but it's not necessary. Is there a recommendation for mastic/thinset/adhesive? DO NOT use mastic, premixed thinset, or ANYTHING that comes ready mixed. Use a good quality latex modified portland cement based thinset. Examples of this would be Custom's Versabond, Laticrete's 253, Mapei's Ultraflex II, or Hydroment's Singleflex. You also want it to be white thinset, as gray will sometimes show shadows through the stone Home Design Expo (where we purchased our tile) says that the process is largely the same. Oh boy. The only similarity is that you use thinset and the same tools. Marble gets set with a much tighter joint (usually 1/16"). Because of that, and the fact that it has a basically square edge, it's very unforgiving with respect to tiles being out of plane to each other. I don't know what they told you about a trowel for setting, but you want a 1/4x3/8" notch. Even with that, you shouldn't be afraid to pick tiles up and either add or scrape a little thinset to get the tiles to sit flush to one another. One other little hint-- DO NOT mesh tape the seams of the cement board before you're ready to set the stone over it. You can then tape the joints, thinset over them, and set the tile all at one time. That way, you won't have "speed bumps" to go over at the seams. You're going to find out just how "similar" setting tile and marble are to each other. :-)

It can be made to work, but I have a feeling it won't be easy, by any stretch. As for sealing the stone to the tub, that's an easy one-- siliconized latex caulking made to match the grout.