This is the ONLY time that greenboard can be used. it's a method of mudsetting showers that's pretty much confined to the west coast, where they put a vapor barrier over the greenboard, and then use that as a base for the mud float coat.

debi, here's the thing: True cement board is made of non-organic "ingredients". Nothing cellulose-based, like the paper facing on gypsum board. Cement board will not degrade when undergoing long periods of water saturation. It will not degrade after repeated wetting and drying cycles like the gypsum core in gypsum board. So does cement board itself have moisture protection and mold resistance? Yes. Because there's nothing organic in it to feed mold, and there's nothing in it that will degrade from water exposure. But you'll note that it does not say cement board is waterproof. It's not. Water can wick right through it. And what's on the other side of the cement board? Your house's wood framing. Again, you'll find manufacturers telling you about their specific product, but they can't say how their product will interact with or protect materials attached to it. So cement board is essentially not affected by moisture. Your house's wood framing will be affected by moisture. Insulation can be affected by moisture. So you have to decide how to prevent moisture generated by your shower from reaching the wood framing or any insulation within the framing bays. Obviously the tile and grout will shed most of the water. But that's why a barrier of some sort needs to be included before residual moisture and moisture vapor driven through the assemble can reach the wood framing. There are a lot of people who build incorrectly. Some through ignorance, some through apathy. Two dollars worth of 6-mil plastic could have solved this before the cement board was installed. You can unscrew the cement board, hang the poly and reinstall the cement board. Or leave the cement board up, mesh tape and mud the seams, then use a topical membrane to waterproof the CBU. Based on the path this thread has taken, I'll toss this out. When you tile, don't use mastic. Don't use any premixed comes-in-a-tub type of adhesive.

debrak: I went to a custom picture frame store and picked out picture frame wood that closely matched my cabinetry. They built the mirror frames according to the size specifications I provided. I took them home and my tile guy did the tile work with the same glass tiles we used as an accent in the shower. Yes, there are tiles on all sides of the mirrors. The only wood you see is a little bit on the front inside edges, but it looks fine because the wood I chose matches my cabinets. The glass tiles came on a mesh type of backing, with space in-between for grout, that can be cut to size. We have two rows of tiles on the front as you can see, and two rows that wrap around the edges. Had the mirror frame been wider, we would have used more tiles--three or four rows. With this frame, however, two rows of tiles fit perfectly. After the tiling was finished, we brought the mirrors back to the frame store, they installed the glass for us, attached a heavy duty wire for hanging, and provided us with hardware (heavy duty picture hooks). I am going to post some more pictures of the mirrors for you to see. I'll take some close-ups of the sides and front so you can see more detail. I'm not home right now and probably won't get to it tonight, but I will try to do it in the next day or two....by the end of the week at the latest. Don't give up on me, I promise I won't forget!

Just to be clear, in case anyone else go the impression this is a steam shower, it is not a steam shower. I will only be taking regular showers with the same amount of heat/steam generated by a regular shower. So there isn't nearly as much steam to purge as with a steam shower. And the showers won't be nearly as long as a steaming session. Also, if I do this I plan to tile the ceiling. This kind of brings up an interesting counterpoint to Sophie Wheeler and rococogurl. A steam shower generates way more steam and never has a fan. According to what Sophie's said any steam shower is essentially a petri disk for mold and mildew because they have lots of steam and no fan. The only difference between a typical steam shower and my concept is that my transom (or gap around two complete walls) will be a few inches below the ceiling instead of at the top. But I'm also generating WAY less steam than a steam shower so, logically, it seems like a reasonable tradeoff. Since my shower is 6' x 4' that gap will be ten feet long by 8-10 inches high. That's a big gap. Is that really insufficient to ventilate the steam produced by a regular shower just because it's a few inches below the ceiling?