He might be referring to "hydraulic cement". Hydraulic cement expands a bit as it cures, it's often used to seal foundation punch-throughs; holes though foundations for plumbing, electrical, septic, and cracks in foundations, etc. "Would you use Wedi, then Kerdi membrane over it (for the steam)? Or is hydroban also ok in a steam shower? " As a stand-alone product in a steam shower, again, Wedi is not appropriate when used with typical tile setting materials (portland cement based thinset and grout). To make Wedi vaporproof you'll need a vapor barrier. That's why Wedi's instructions specify using epoxy adhesive to set the tile and epoxy grout when using Wedi in a steam shower. The epoxy will be your barrier. If you don't use epoxy then you'll need some other sort of vapor barrier within the wall system. Wedi ($$$$$) plus epoxy adhesive ($$$) plus epoxy grout ($$$) is an expensive way to go in a steam shower. Kerdi membrane is a vapor barrier by itself. But Kerdi membrane over Wedi board is not an efficient use of your monetary resources. Anyone offering that idea? They're not looking out for your best interests. Regular old 1/2" Durock (or equivalent) cement board covered with Kerdi membrane will give you a water and vapor proof system at a fraction of the price (roughly 1/3rd the price) of Kerdi over Wedi. And you can use portland cement based thinsets and grouts. The same with Hydroban. Hydroban by itself is not a vapor barrier. If you use Hydroban in a steam shower you'll need a vapor barrier somewhere else in the wall structure. Hydroban, however, is a fine waterproof membrane for non-steam showers. So for the products you mentioned; Wedi, Kerdi, and Hydroban...for the "best performing" structure with most efficient use of resources, for a steam shower I'd use Kerdi over cement board with portland cement based thinsets and grouts. For a non steam shower I'd use Hydroban over cement board with portland cement based thinsets and grouts. If you really want to use a Kerdi "Board" or Wedi "Board" for the sake of using one of the fancy and expensive "boards", then for the steam shower use Kerdi Board which is water and vapor proof. For the regular shower use Kerdi Board, or use Wedi Board which is only waterproof. If you really want to use epoxies, then have those as well. Epoxies are generally overkill in residential construction. My opinion. In a commercial or in a very often used residential shower or steam shower, they may have benefits. But don't let them up-sell you on those products just because they are the "latest and greatest". They are fine products. They may have their advantages for certain design requirements. But they can also be inefficient, and even a liability, for other design requirements. Realize that the vapor-proof and water-proof comments I made regarding the specific products mentioned are fact. But my recommendations are simply my opinion. I have no aversion to spending more money if required for better construction. But I'm not one to waste money.

In my unusual installation adventure last year, I noticed that the price was about double or close to it. I ended up with a totally free low iron french door shower enclosure. Millworkman was very helpful in problem solving some issues with my glass. THANKS! If I had another room to do I'd consider the regular glass as an option. It really depends on the colors in the room. I have blues and greens in my bathrooms and the regular glass would go with it just fine IMHO. My drama from several years ago: beautiful-but-ugly-shower-doors

Oh, I didn't realize you wanted to run both the rain shower and regular showerhead at the same time. Check your state and local codes. In California, where I live, building inspectors usually won't pass multiple simultaneous outlets anymore due to the new water regulations. The age of the "human car wash" spa shower is over in CA, lol. Even if each outlet was limited to the national 2.5 gpm, they often added up to 10 gpm or more (old showerheads used to flow about 5 gpm). The Hansgrohe three-way "green" diverter I used met CA code because only one water source at a time could be selected. A non-green code version is available too, but I didn't may any attention to the details because I can't use it here. The advice to use 3/4 inch pipes instead of 1/2 is good, though I am not well versed on the pressure loop concept. We've always had good water pressure in our house (city water supply and a not-very-old pressure regulator). Master bathroom and hall bathroom's pipes are within a shared wall. We removed all the 1/2 inch copper supply lines and replaced with 3/4 inch PEX while the shared wall was exposed during the first bathroom remodel (1/2 inch PEX from supply lines to each outlet). Water pressure is as good as it's ever been, even with reduced flow showerheads (Hansgrohe Raindance @ 2 gpm). One way around the issue of two shower sources going at the same time in the same shower area may be to have a controller/valve for each shower spray source, because then it's no different than two people showering at the same time but in different bathrooms. But check with your building department just to be sure. And the cost of two valves, two trim kits, and additional labor is higher, so you'll have to consider if having both showers spraying at the same time is worth the extra expense.

My fixtures are Phylrich but I don't think it is the manufacturer but the type of valve. I suspect that pressure balance valves might be more "mixed" and therefore not be as cold as your unheated water might be. The thermostatic valve has advantages and more control of temperature is probably one of them. At any rate, I would suggest you go to a really good plumbing store with lots of choices and find something there.