Thank you Mongo for the explanation. It came just in time. I just had two other tile guys come in today and YOU WILL NOT BELILEVE...okay you pros out there probably will believe...what I heard today. When I mentioned what the original installer said, I think David you called it laziness, Mongo you called it uneducated. Here's what I found out. I had two additional tile installers out today. I was still not hearing what I wanted to hear when I asked for details about their process, esp. regarding the moisture barriers behind the cement board and the membrane on the shower pan floor. The last guy seemed very knowledgeable and I said to myself, I've got to come on out and just point blank ask because I am not getting anywhere. He said the same thing about cement board as the previous guy, but at least HE mentioned, taping those seams of the cement board with a mesh strip and thin setting it. So far so good. I asked about some other moisture barrier for the framing before cement board. He said they use a poly liner thing behind the cement board on the exterior wall. They don't normally do it on any other wall but they could... no problem. He mentioned some of the new boards that are lighter and made of foam, but he said they don't use them. Same deal, unproven and he would prefer cement in his own home. We talked about the shower pan membrane and he too talked about sand mix, membrane, build slope and tile. I finally came out and said, "I read somewhere the membrane should be put on a slope or something." He said we generally do it flat but what you are talking about is the pre-slope. He KNEW ALL ABOUT IT! What he said next floored me. He said yes in the Highland Park area we do a preslope. They have million dollar homes there. Not to say your house is not nice, but that area has more restrictions. Mongo, David and Bill...he described the steps just like you said...I guess my less than million dollar house didn't warrant the "correct" installation technique. :-( He even said why it is better to put it on the preslope, but I guess "cheap" houses don't get the extra steps. LOL I asked him about the membrane placement and he described what I had seen in the Harry Dunbar website. He did say he goes up about 8" on the walls, not 12 inches. He did say doing the preslope would make the shower pan area higher, but I told him I did not have a problem with that as long as the membrane was on the preslope. He did not have any problem doing it, but I am sure it will be reflected in the estimate he gives me. :-( Thought you guys would be interested in what I found out today. Thank you so much. I definitely will not be using the first guy.

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...

The detail you're trying to achieve is the same as using a topical membrane for a tub surround. Hopefully this drawing will post, it's from a thread several years ago. Although this drawing was to depict Kerdi, it's pretty much the same for a topical liquid membrane like HB. For joints, Laticrete specifies using fabric to bridge certain seams. You can use Laticrete fabric or anti-fracture membrane to bridge the gap from the cement board to the base flange, applying HB as needed. It's the same idea that you originally had using Kerdi to bridge the gap. I fully understand Laticrete, or Schluter, or Nobel, or whomever, saying they don't make a product for this application. They do. The products will work. They simply can't acknowledge every possible variation in an installation. With all that written, look at the drawing again. If the wall tile is standard sized tile, a good portion of the tile will be bonded to the membrane that is directly backed by cement board. An inch or so of tile will be bonded to the fabric/membrane that is floating over the cement board-to-flange gap and down over the flange. That's fine. Where you can sort of run in to trouble is if you're using a small mosaic tile on the walls and you want the mosaic to extend down over the flange. In an installation like that, you could have issues with the bottom course or two of mosaic, as they'd only be bonded to the fabric that's bridging the gap. In a case like that, I'd shift gears for a slightly different approach. That's the reluctance of any manufacturer to say their product will work. Their product can work. But there are so many variables in installations that for sure someone will bugger it up and bad mouth the product used in the failed installation, even though responsibility for failure lays with the installer rather than the product.

If you'd done the shower in 2014 or earlier you'd have been approved by schluter and the tile gods at TCNA using reg kerdi. Standards have changed , but that doesn't mean that all those with the old standard should rip em out or are going to experience premature failure. Sure , the lower perm rating is better- but it's not a free lunch. I wouldn't worry about it in a residential setting that doesn't get heavy use. And I'm putting my money where my mouth is. I have a steamer done with kerdi circa 2012 and it isn't coming out, and doesn't show any signs of failure. It's used approx 3-4 hours a week. Like CT said , it was done ( and good enough) like that for years prior to this. Using kerdiboard plus another membrane on top is a no no.