The moldy part doesn't look like cement board to me, it looks like drywall. Are you positive it is?

It appears that the lower board is wicking water from the pan. Georgia Pacific's DensSheild virtually doesn't wick, but drywall can.

This post was edited by Trebruchet on Wed, Jan 1, 14 at 10:54

How to proceed - you are going to have to tear out and redo the RIGHT way. I hope you can track down your contractor. And even if you can get him to redo it for FREE, can he or will he redo the shower the correct way.

There are two ways to handle shower walls - plastic on top of the framing and then cement board and then tile. The second is cement board then a topical paint moisture barrier like Red Guard or Hydroban or a plastic type fabric installed like wallpaper such as Kerdi (or Kerdi knockoff) and then tile. Now Kerdi can be applied to drywall and is warrantied so. Kerdi is bright orange. Hydroban is greenish and Red Guard is pink/red.

Study up on these methods and make sure one of them is specified in your contract. And take pictures - always take pictures of each step before the walls are closed up.

You can search this forum for Kerdi and Hydroban. Good luck, I know this isn't fun for you.

This post was edited by Anna_in_TX on Sat, Dec 28, 13 at 22:04

Plastic (I'm assuming you mean vapor barrier) on top of studs with cement board and then tile is about the worst way to install shower tiled walls possible. Grout and cement board are porous and water will wick right through, including through the screw holes in the cement board/vapor barrier and right int the wood. It will also move down behind the cement board and into whatever wood structures are behind/below the shower.

If I've misunderstood what you mean by 'plastic' on top of the framing under the cement board I apologize, but I can't think of a single method of putting a waterproof membrane between cement board and framing.

The only way to do a shower wall is by waterproofing between the tile and the substrate, be it cement board or whatever you use. Not much beats Kerdi fabric but painted on Red Guard is fine too.

The waterproofing on the wall continues and integrates with the waterproofing method used for the shower floor and all tying into the drain.

2 years later no contractor is going to waltz in and re-do a bunch of work you already signed off on and paid for. If you agreed to their methods/materials/processes in the first place then you're out of luck. Tens of thousands of 'professionals' still slap cement board on top of wood framing and then just tile on top of that. There's no 'right' or 'wrong' way to do this, just 'good' and 'bad', and there's no law saying if you choose the 'bad' way to do something you have recourse 2 years later.

TorontoTim,

I suggested the vapor barrier behind the cbu as an alternative method to Kerdi/Red Guard/Hydorban/ect only because, at least in my area, it is difficult to find a lot of tile guys who work with these methods - even Red Guard which is easily available at Home Depot. They may be set in their own ways, laziness to learn new methods , or time. You would be surprised how many builders are installing tile on straight cbu - and the reason they are using cbu verus greenboard is the relatively new code.

Ladoladi,

I suggest you educate yourself with the various methods of building a shower by searching this forum.

Using a vapor barrier behind cement board is an accepted practice. The cement board does absorb moisture through the grout and takes longer to dry out versus putting a moisture barrier on top of the cement board. And the moisture barrier on top (Kerdi, Hydroban, Red Guard, etc) is the best method.

If you go with a cultured marble shower, ensure that the framing and the marble slabs/pan are level, flat, plumb, straight, "true", etc. Make sure the shower components fit well together and the corners overlap well. Cultured marble is made by hand and manufacture quality and installation are dependent upon the individual shop. You will have to maintain the caulk on the seams on a regular basis (especially after seasonal temperature changes) because that is the only thing keeping the water from getting back behind the walls. The pan does have a lip. A good shop should install the cultured marble on cement board with a vapor barrier behind that. If your marble is light colored, you can paint the cement board. I do not know if the cultured marble can be installed on a moisture barrier that has been applied on top of the cement board. That would be a better way if it can be done - but so many of the cultured marble shops still install cultured marble on greenboard type drywall. (I had the cultured marble shower from hey installed by my home builder and learned all the wrong ways to build them.)

Good luck with whatever you decide.

This post was edited by Anna_in_TX on Tue, Dec 31, 13 at 21:49