No way, no how. If it were a tub, I'd chance it with the Kerdi. But even though Schluter will warranty it, I wouldn't even chance it in a shower with Kerdi. That drywall would be coming out. End of story. If you're not going to take it out, though, Kerdi's the only choice.

Yup. Redgard over drywall is a no-no.

Mongo

Even more fundamentally, Isn't drywall a no-no in a shower area???

Our installers did some pretty bizarre things for preparation whilst we were at work that we learned about later. But fortunately even they knew to use cement boards in the shower areas.

Mindstorm-- as far as I'm concerned, you're right. However, Schluter will warranty Kerdi over drywall, and from the sounds of the OP, there are some who now think that applies to ANY waterproofing. Personally, I won't even trust Kerdi over drywall in a shower, much less anything else.

Thank you all for responding to my plea for help. I spoke with a local very well respected CG yesterday who said that he always installs "turf rock" before using a liquid membrane. Sometime later today I will be speaking with "the best" tile installer around these parts - it'll be interesting to hear what he has to say. All indications are that we will be removing the drywall in the shower and going with something more suitable for the job. For the bit of tiling that will be vertically applied around the tub deck, we'll probably leave the drywall and Kerdi there. There's no way I want to take any half measures in this area and invite potential problems later. If any one has further thoughts/comments, bring them on!!!

What is "turf rock"?

alliemacdee,

Turf Rock or "ToughRock" as a tile backer in a wet area...still, find out what membrane he's going to apply over it. Then go to the membrane manufacturer's site to see if it's an approved method.

Sadly, being "experienced" or "well-respected" in construction really doesn't mean that things are done properly.

Some builders just "build". Others "build professionally", meaning they continually educate themselves and their subs regarding approved methods and discard unapproved or outdated methods.

Friends built an $11M absolutely gorgeous ski house out in Colorado several years ago. Sadly, it's falling apart from inside the walls out. The GC totally screwed the pooch on it. But it looks great, and he's well-respected, and even the president of the local building council. But apparently he doesn't know squat about vapor barriers or the difference between open and closed cell insulation. To him, foam insulation is foam insulation. And that lack of knowledge will cost him dearly. It will probably bankrupt him.

Mongo

If you can find a tilecontractor that still knows how to float(that is to paper, wire,and cement the walls)you will end up with the best job possible.

A mud job is always the best way. Flat, plumb, level and square, with wire reinforced corners-- no way around it-- it's been around for thousands of years, and will be for thousands more. However, not all people can afford to install with a proper mud job, not to mention the fact that most structures these days aren't engineered to take the extra weight. That's where CBU comes in, and the Kerdi can be used EITHER way.

By the way, welcome to the forum. :-)