Soonermagic, Kerdi is the perfect choice for a steam shower. No if's and's or but's. Here's the deal as best as I can describe on the forum...what follows is not a perfect description, but generalities: Unmodified thinset cures via a chemical reaction. Essentially, it does not need air to cure and harden. The chemical reaction consumes water in the cure. Put a dollop of unmodifed thinset in a zip lock bag and it will still cure and harden. Add a latex modifier to the thinset for lightly modified thinset? You still have the "no air required" chemical cure for the thinset, but the latex modifier needs exposure to free air to dry. No air, it'll remain slightly soft. Highly modified thinsets need even more exposure to free air so the additional latex modified portion of the thinset can fully dry. Put a dollop of highly modified in a ziplock bag and it may not fully harden, even after several days. What is Kerdi? A polyethylene sheet membrane. Air can't pass through it. Air can't pass through glass tile either. So a modified thinset will take longer to cure and harden when sammiched between Kerdi and glass than would an unmodified thinset. Small glass mosaic tiles like yours have a lot of grout joints, the modified thinset can "air dry" through those joints. It may take longer than glass over cement board (air can pass through cement board), but will usually eventually dry. This is why Kerdi recommends using non-modified thinset in a lot of their installation documents. It depends on what you're tiling, the size of the tile, etc, but in general Kerdi recommends non-modified, or "dry set" thinset. Glass tile, being smooth, needs something that will grab and hold it. That's why most glass manufacturer's will recommend a modified thinset to adhere glass, as the modified has better bonding properties and has a bit more flex to it, meaning it's bond is not as brittle as a dry set bond. Therein lays the conflict. I've installed a lot of glass over Kerdi. You just need to know what you're doing before you attempt it. It takes a bit of reconciliation between the tile installation instructions and the Kerdi instructions, with a bit of common sense thrown in. Tilers need to better educate themselves before attacking installations like yours. Tile products have evolved over the years, and continuing education is the difference between a true professional and someone who just shows up to work with his lunch pail. I'm not necessarily knocking your installer, but your GC and tiler should have been on top of this long before the first batch of thinset was mixed. Best, Mongo

"My contractor used mastic everywhere he installed new tile for me--kitchen floor, foyer, etc. Is it okay in these areas since they aren't generally wet, or is this still a no no? " Laila, it depends. On your substrate and the size of the tile used. Substrate: Some manufacturers restrict the type of material that you can spread mastic on. Example, many prohibit OSB and chip board types of subfloors or underlayments. Tile size: Mastic cures by drying, so it needs exposure to a certain amount of free air. Some restrict the size of the tile you can install on floors and walls. Floors size is usually more restrictive due to the weight of walking on the tile. If the mastic can't see enough air the mastic can remain soft. One mastic I've used has I a maximum of 6" square tiles on floors and 10" square on walls. Another manufacturer restricts tile to 12". Some prohibit setting natural stone tile on floors with mastic. So within the entire family of mastics, each manufacturer may have their own limitations due to how they formulate their specific products.

When you said that the labor is ALOT more time consuming, does that mean you have to be more careful cutting and setting the tiles due to the "less forgiving material"? That's part of it. When it comes to stone, especially polished stone, if it's not perfect, you'll see it, and you'll feel it. I've said many times it's all in the reflection, because reflections don't lie. Look at the picture above of the reflection in the shower wall tile. See how the reflection is continuous from one tile to the next? If the tile isn't set perfectly flat, that reflection will be broken all to hell. That takes alot of time (as well as alot of skill) to get it that perfect. I don't mean to be tooting my own horn here. I'm trying to help you understand why the need for the extra time, and therefore, the added expense. Just because someone can set tile, doesn't necessarily mean they're competent to set stone. what marble was used? Any sense of the cost of materials? The white is carrara, and although I'd know the name if I heard it, I can't remember the name of the grey marble mosaics. As for cost, the carrara isn't much (as marble goes!)-- maybe 6-7.00 a foot. The chair rali, pencil liner, and mosaic listello, on the other hand, are a different story. Each chair rail and pencil liner is about 22.00 a piece, and the mosaic listello's 32.00 a foot. so for every linear foot of that wainscot, the price is 76.00. This is not exactly an economy bathroom! LOL I know the greymosaics weren't cheap, either, and they're also used on the floor for the "dots" as well as that piece on the wall.

Kerdi Update: I've gotten a couple of emails regarding the newer "Kerdi-DS". First, emails. I often get emails sent to me through the G'web email system, and because of the sender's setting on his/her G'web account, those emails can not be replied to. So don;t think I'm rude for not replying to your question. More often than not, it's literally impossible for me to reply to your email due to your account settings. Kerdi-DS. What is it? It's simply a thicker version of plain ole Kerdi. Kerdi is 8-mil, Kerdi-DS comes in at 20-mils thickness. Why is -DS now getting attention here in North America? Because TCNA has changed their recommendations for membranes used in commercial or heavy use steam showers. Recommendations for residential use steam showers have not changed at all. What or who is TCNA? TCNA is the Tile Council of North America. You might see references to TCNA when it comes to installing tile. TCNA publishes "best practice" guidelines for tile installation. You have an organization like TCNA which is fairly nimble when it comes to changing recommendations for installing tile. Then you have "building code", which only gets updated every few years, and updates are subject to influence from various interest groups; be they trade groups (plumbers, electricians, etc) or large corporations that make building materials. TCNA will often make tile/shower/bath recommendations that improve building practices several years ahead of those changes being implemented into state or national building codes. Blah blah blah. So what is this about? We have water barriers, which limit the penetration of liquid water. Then we have vapor barriers, which limit moisture vapor penetration. At a minimum, a water barrier is needed in a shower or tub surround. A more robust barrier, or a vapor barrier, is needed in a steam shower. Protection from vapor penetration has been typically defined by a product's "perm rating". Previously, if a product had a perm rating of less than 1.0, it was considered a vapor barrier. Example, a topical membrane that I use often is Hydroban. Hydroban has a perm rating greater than 1.0, so it can be used as a waterproof membrane in a shower, but it won't suffice as a vapor barrier in a steam shower. A product like RedGard has a perm rating of less than 1.0, so it can be used as a waterproof barrier in a regular shower, or as a vapor barrier in a steam shower. Kerdi? "Regular" Kerdi, the "standard" 8-mil thick Kerdi, has a perm rating of around .90, so it can be used as a water barrier in a regular shower, or as a vapor barrier in a residential steam shower. TCNA has revised their recommendations for vapor barriers used in heavy use or commercial use steam showers. Health clubs, spas, etc. Whereas the old recommendation was to use a material that simply had a perm rating of less than 1.0, for commercial installations like listed above the recommendation has been...