With the darkened grout so high up I would think the tile was dot or spot set. Most likely drywall as a backer board.

I honestly don't know what material was used, but I know it wasn't drywall from when I visited during construction. Don't recall if it was the orange synthetic backer board or a concrete backer board, but drywall wasn't used (I made sure if it due to another builder using drywall in a prior home and me having to strip the shower and re do it)

I can't imagine fixing this topically. Not permanently anyway. Bottom row of tile's gotta go.

Jerzeegirl - what ended up being the moisture issue in your case?

When my house was built, it was okay (code) to use green sheetrock, which must have been constantly getting wet and drying out over the years. The grout would get black in certain locations and we thought it was just dirty. After a while we realized that it wasn't dirt, it was moldy. My tile guy also told us that he wouldn't be surprised if roots had started growing up through the slab because he had seen that happen before. Luckily we didn't have roots. He demo'ed the whole shower and treated the studs with mold killer. Then gave us a wonderful Kerdi shower. There have been absolutely no problems ever since.

Looks like the used cement board and no water proofing so it holding moisture

A properly built Kerdi install usually solves the issues.

Sorry I don't drink the orange schluter cool aid. I don't believe in the product. 95% of all the work we preform are mudset jobs due to tight tolerance of the material. You can't do a mudset job on schluter substrate and there is only a 2 year limited warranty with Schluter. On top of that it is way overpriced.

Probably because you don't NEED a mudset job on a Kerdi Shower. If the framing and walls are true, why the mudset? Make no mistake, I have done tons of them and they certainly are great. Straight, plum and true.

As to being "overpriced," yes, there is a proprietary drain assembly....which looks MILES better than the average PVC/FHA $9.00 drain and will cosdt you a hunnerd bucks or so. (big whoop!)

When I factor in the time differential of mudding walls, putting in a preslope, setting and folding a rubber liner, metal cladding the curb for fat mud, putting in a final slope....all before you tile, as opposed to simply ONE mudbed, Kerdi the walls and floor and tile away...in many cases, I'm less expensive than the "Traditional" way...simply because of time.

Warranty? Don't care about the Company. I warranty my stuff for life...and have yet to have a callback. What is "Life?" Until either you die of I die.....lol

Oh, and by the way, you certainly CAN use Kerdi on a mudset job.

I spoke with a sales man for schluter and I told him most of our jobs were mudset and the foam board I thought was so flimsy. He said that schluter doesn't recommend mudsetting your material on top of the board but instead correcting the frameing prior to installing board and then installing the tiles using only thinset.

Regarding Kerdi and mudset. I'd never float mud over kerdi, or kerdi board. I agree that that type of installation makes little sense. Practical or financial. I'd guess that from the technical point, the weight of the mud might even be too large of a shear force on the fleece membrane, not to mention possible adherence issues of mud-to-fleece.

If someone wanted a topical membrane I could see using Kerdi or some other sheet or liquid membrane on the wall after floating the walls. And that's Kerdi membrane, not Kerdi Board.

If 95% of your work is mud walls, then you really have no need for Kerdi, especially Kerdi Board. No argument there.

So the builder is now saying that there's record that the bottom row of tile had been removed and replaced with new grout, which he claims he's confident is the reason the grout s discolored. Looking at the pics (and seeing in person), this doesn't at all look like a "different batch of grout".

He's "willing" to open the wall from the rear through the drywall to confirm there's no moisture problem, but from the above it seems like a moisture issue wouldn't be noticed going this route since the moisture would not be on the back of the cement board, which is all you could see by opening the drywall on the other side of the wall, but rather a moisture issue between the tile, grout, and water barrier, correct? If I removed some of the discolored grout, would I be able to notice a moisture issue that way?

Same advice you got at JB Forums.....

Haven't seen a reply to this question posted tonight on JB. Which advice are you referring to?

Any thoughts from anyone on the latest? Can I see if there's a moisture problem just by removing grout?

Does it HAVE to be moisture from behind? Can't it just be soap scum and water that has turned moldy? When I looked at your picture, my first though was to spray that with Tilex (mold & mildew - not tile cleaner) and let it sit. I bet when you go back an hour later, the grout would be clean again.

Debbi - I've used Tilex, Finnazle and a couple other soap scum removers and mold/mildew removers multiple times and none of them have had any effect.