Walls outside the tub surround will typicall be covered with 1/2" drywall. Inside the tub surround they should be covered with 1/2" cement board, or some other 1/2" thick code approved, wet area tile substrate. Have the joint where the drywall and the cement board meet fall behind a tile. The last row or course of tile will mostly be on cement board, but enough of it will still cover the transition from the cement board to the drywall to give you a seemless transition. Mongo

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.

jcorn1 - Glad your test was successful! And sorry to hear about your friends problem. Curious though as to how they knew it had a leak when the tile had been started, but not finished. Did they do a test then with only part of the tile laid but the shower not finished? Was their install done by someone with Schluter experience or was it a DIY job? Just curious. I will have a water test done by the tile setter, but I doubt it will be a 48-50 hour test! What I may do is a test of my own for that extensive length of time AFTER the shower is completed. I have a one year guarantee, and if that shows a problem, I would call them back quickly and make them rip it out and redo it. And hopefully we could still get extra tile to match the rest of the room at that point. Not sure about the Schluter warranty info you got over the phone. All I could see on their website was info saying that doing such a test was "recommended". I looked at the warranty info on their website and didn't see anything specific about a water test; it just said material had to be installed in accordance with the handbook and "industry standards". The install handbook says that water testing is "strongly recommended to verify a successful installation". I guess they would point to that, but other sections of their website and literature make a big deal about how you can set tile right away. In one place, it says water testing MAY be performed and says it is a BEST PRACTICE. And the water test is technically not part of the install and would not affect the outcome - its just a way to verify a good install. It could be that if water testing is required by local code, they would point to that as a reason to void the warranty, but otherwise I think it would be a tough argument. In any case, there's no way I want to experience a failure after the tile has been laid, so I agree that it's good insurance - but definitely not a 100% sure thing if failure may only show after 50 hours!

Thank you, very kind words. I am actually very proud of how well it came out, being my first ever vertical tiling effort. The only slight lippage there is, and its not really noticeable is the bottom row where I couldn't use tile leveling clips due to the ledger board. But I'm probably the only one who will ever know it's there. I really enjoyed the large format on the walls for a couple reasons. I was going for a marble slab look and that was the best way to go about it. Few grout lines was another reason. And lastly, just fewer tiles to hang. But putting large tiles up made me very grateful I spent the extra time and effort to make the walls plumb and square. I do love the schluter corner shelves. Sure beats the (in my opinion) dated look of those big bulky tile/carrera corner shelves. The top two are the same model Shelf-E squared off and the bottom is a Shelf-E triangle for my wife to put her foot to help her shave her leg. BTW....the best investment I made for tiling was a suction cup. Absolute game changer.