If he does mud walls, is something else needed though (on top), besides the paper behind it? No, just as with a thinset installation, all that's needed is the vapor barrier, which is what the tar paper is. This where the advantage of the Kerdi comes in. WIth a standard mud or thinset installation, the sub surface still gets wet. With Kerdi, being that it's a waterproofing membrane that sits on top of the mud of cement board, the only thing that gets wet is the tile and grout. And by a conventional pan on the bottom, do you mean doing a mud preslope, membrane, then mud again?, then thinset and floor tiles? Do I have this out of order or is there some other layer that needs to happen in there? no, you've got it right. OR, we could see just how good a mud mechanic he is, and see if he'll set and grout it the same time as he floats it the second time! :-) That's a TRUE (monolithic) mud job. *stirrin the pot* I got to proof reading this, and I had to add this disclaimer-- If he's doing thinset over the mud, that's the normal way it's done today, and there's nothing wrong with it, so don't get scared if he brings in the bags of thinset!! :-)

Hard post to reply to. If you want DIY-friendly and cost-friendly? Durable? Look at cast iron shower pans. You'll spend $400-$800 on the pan itself, HOWEVER...once the pan is in, there's your shower base. Done. Clean, nice looking, easy to clean, durable, zero flex underfoot...DONE. There's nothing else you need to spend money on regarding the shower floor. It's done. And a travertine porcelain would look right at home with a cast iron base. Again, with economy in mind, on the walls? I'd staple up 6-mil poly sheeting on the walls. $10-$20. Cover that with 1/2" Durock cement board. $150+/-. Add a roll of mesh tape. $5. Then tile on the cement board. Your tile can be as inexpensive or as expensive as your budget allows. Grout, and you're done. If you want to upgrade your waterproofing a bit, and can afford another $150-$200? Then instead of installing the 6-mil poly, just install the cement board directly to the studs. Then use a waterproofing like HydroBan Liquid or RedGard on top of the cement board. Read the instructions. Follow the instructions. If you can't, then revert to the first set of instructions that used the 6-mil poly. Then tile right on the Hydroban or RedGard. Grout.

Metricpony. If the current sub can't fix the work they installed, I would consider someone else to do it right. I would imagine the builder will object to getting a new installer, but the bottom line is, you have to be happy with the finished product. I understand what Weedyacres said about putting waterproof membrane over green board and it being suitable, but I don't believe it's something that's going to last for years. There is no reason to rip out rows of tile, just to install a listello to make the job right. It should have been set up right to start with. This is just an installer that doesn't care how it ends up. Any professional would have done a lay out to make sure it falls with a full piece or a nice sized cut. Personally, if it were my house. It would all be removed and start over using cement board and an installer that cares about the work they do and the finished product.

Wedi is A great system . I have installed many wedi showers. Heres a few things I can share. If your tiler Installed all of Wedi Properly and used The *****PROPER WEDI brand sealant ON EVERY SEAM., the system is very solid. A wedi shower build mixed with porcelain or dense glazed ceramics and good grout will Dry out very fast after use, this means they dont retain much water if installed correctly. Things like the pan being set level, mortar selection and application, 98% coverage and proper key in. followed by pure silicone changes of plane and its pretty much a home run for me. If you called me to your home to investigate this problem, id first get a complete and detailed list of what CLEANING CHEMICALS you tried several of..... id politley advise you , you may have worsened or created this issue. :):):).... and how you applied them and removed them and mixed them. There is a reason we use Tile specific cleaners in showers and other than the Vinegar, Dawn, baking soda type remedies I dont veer to far outside of using ANY cleaners that aren't specific for the tile/stone and grout you have and I wouldnt be online taking random advise. I 'd call the MFG of wedi, or the Thinset/grout MFG, or the, Sealers/cleaners MFG Tech support. This is how the tile pros deal with these issues, direct from the horses mouth when problems arise. What I would be be looking at ( after what chemicals have been introduced) Id be asking for pictures of setting materials used to set all the tile, Id inquire about curing and dry times and focus on the possibilty you may have either latex leaching from a latex based caulk in the assembly, Or A Bucket ready mixed setting material in the vien of mastic or a new age grout not meant for submerged applications. Could be as simple as Using latex sanded grout caulk in the pan that will mold. Rest assured body and soap scum, in a properly built shower with the properly applied materials would have a real hard time producing this effect in a Wedi or topical waterproofed shower. . How is your bathroom ventilated? the fan runs after each shower? the windows get opened? etc etc..... Eliminate what chemicals you used that may be causing this and inquire about Grout, mortar, mortar coverage, Sealants at change of plane and the proper Wedi sealant was used. If your installer wont help you here id first call Wedi and request a site visit from there rep. My free advice to you based on My years of hands on Industry proven tiling experience and Wedi expertise.. -best