For the past 20 years we have used ditra as a substrate on all floors. It is great to work with and helps create a fantastic bond and as a decoupling membrane so that when substrate moves tile won't crack. As far as shower walls we only use hardibacker these days- not wonderboard. Installed properly with paper this makes it very tight to top it all off although harder to use and more expensive we use epoxy grout on everything. It makes things impenetrable. It never changes color and works as a sealer over the whole projects. We have done hundreds and showers and floors and I can't think of the last time we had a call back-- and we are huge on customer service.

Hope this helps.

Thanks for your response. Hardibacker = cement board? That's not what my guys have used - it's the Certainteed moisture-resistent gyprock that's on the walls. And Ditra is the Schluter membrane, right? And yes, epoxy -- we have talked about that; I will remind them.

Where is the humidity-resistant gyprock installed?

Yes ditra is the schlepper membrane and no hardibacker is not cement board, but your system probably works fine, just not what we do. If you have a reputable tile man he should be able to guide you through failing substrates, cracking tile and improper adhesion - the best advice I have to give you is after all those things are done is to use epoxy grout. It holds everything together and keeps color looking great for years.

@PPF: against the wooden studs?

@Toupin: thanks!