We need more info -- what was the construction method? what kind of waterproofing? how was the curb built? what kind of shower pan? Type of thinset used?

Not sure what you mean by the construction method.Can't really answer your questions--we did not observe construction as we were at work while the contracter was in our house.

Curb movement like that is typically from a wood-built curb (stacked 2-by lumber, for example) that is absorbing moisture and expanding/swelling.

How is moisture getting to the curb? Could be one of several things. Not sure how conscientious the installer was in terms of making sure the shower pan membrane is sloped (versus laying the membrane flat on a flat subfloor), or how he detailed the membrane over the curb.

It's possible there are nails through the top or inside faces of the curb (and thus through the membrane) and moisture is getting through the nail holes.

It's possible that he built you a perfect curb but used wet pressure-treated wood and the PT wood is warping as it dries.

Or your house is on a slab, and he put the wood right on the slab. Moisture through the slab is causing the wood curb to expand.

So it could be one of several things.

It should be fairly easy to diagnose though, as the tiles are popping off on the outside face of the curb. They'll have to be removed eventually to diagnose and repair.

When they are removed, take a look to see what's in there. Post photos if you can.

To give you a bit of an education as to how a typical CPE-membraned shower with a wood curb is built, check out Harry's pictorial.

Note that Harry's membrane is "draped" over the wood curb. That there are no nails/screws on the top or inside face of the curb. That the lathe (wire mesh) is bent in a "U" shape and it's simply the inverted "U" bends that hold it over the curb. Again, there are no fasteners through the lathe and into the top or inside face of the curb.

I have seen instances where the membrane gets draped over the wood curb, then the installer nails cement board on the three faces of the curb and tiles on the cement board. Not good. Again, nails through the membrane on the top and inside face are a no-no.

I don't see screws through the bottom track of your door frame that go into the curb. That's good.

Best, Mongo

I'd forgotten that my husband took some photos before the tile was laid. Here is s photo of the shower curb prior to being tiled.

Regarding the slope of the floor, our previous shower leaked and the contractor assured us he had sloped shower floors a hundred times and that it would never leak.Just FYI, we picked this contractor because he came extremely highly recommended by another contractor/landlord who uses him in all his rental homes and construction projects.

The bathroom is on the second floor of our house which has a cedar tongue-and-groove subfloor. The contractor examined our floor carefully due to previous leaks (wanted to make sure the floor wasn't rotten) and he said the subfloor was good. (He had previously repaired part of the subfloor in our living/dining area prior to having that area tiled, and we have had no problems there).

Just looked at Harry's pictorial--looks like there are screws on the outside of our curb that are not in Harry's pictorial. Unfortunately there are no photos of the inside of the curb--wonder if there are screws there.

The screws on the outside of your curb are fine, the fact that he used caps makes me think he's not a hack.

But the curb is swelling, so something is wrong somewhere.

I'd ask how your guy detailed the membrane at the inside corners where the curb meets the wall. Sometimes the membrane can be folded over on itself to create a watertight corner, sometimes the membrane will be cut to conform and lay flat over the curb corner, then a preformed corner will be glued over the cut membrane to provide a watertight seal.

One other thing...can't tell from your photo, but I'll throw this out for reinforcement. The floor membrane needs to be sloped. It's a code requirement. Some guys lay the membrane on the flat subfloor then put a sloped layer of deck mud over it.

The proper way is to put a sloped layer of deck mud on the floor, then put the membrane on the sloped deck mud. Then another thickness of deck mud goes over the membrane.

I'm not saying your guy did "either or", but these wll be points of discussion when you have him over to discuss the failed curb.

Lastly, every once in a while there can be a leak in the plumbing within the wall. Where the shower arm screws into the wall, for example. In a situation like that it'll only leak/drip when the water is running, but water can run down the back of the cement board and be funneled into the shower floor structure. Not likely, not often, but again, it's a point to ponder.

Thanks for the further insights.

I'm also glad to hear our contractor is not looking like a hack. :-)

I just talked to my husband, and we both think the contractor sloped the floor, then laid the shower pan over the sloped cement, then mudded and tiled over that.We're not 100% sure and will definitely bring this up.Also, my husband thinks the shower pan corners were folded. We will ask about these possible issues, thanks. Is one way (folded vs. cut with preformed corners)better than the other?

We had water running down the back of the wall in our other bathroom where the tub spout was set in;silicone around it solved that problem. I suspect similar problems are not happening in this shower, only because on the wall where the shower head and water controller are set, the grout looks completely dry. We'll keep in mind that it's a possibility, though.

Do you think the contractor will need to take up the tile on the shower floor, or is that hard to determine at this point? As I mentioned, we are afraid of doing too little and having a "quick fix" that only lasts for a brief time.

On second thought, now that we (DH and I) are looking at the photos again, we are wondering:

In the photo showing the curb with the liner and srews on the outside, should the liner also be visible on the shower floor? It appears like it might be cement showing on the shower floor with liner over the curb. Would that necessarily mean that the liner was placed down flat first, then the cement sloped on top, like you said was the wrong way to do it?

Cut versus folded, in the shower corners they are almost always folded. At the curb, it can sometimes be a compound fold, so sometimes a preformed corner fits the bill. Both are fine.

A curb repair can usually be made without having to demo the shower floor. As always, it an "it depends" scenario. But again, until the cause of the failure has been identified, it's a guess.

There should always be deck mud over the pan membrane. But when using a membrane like yours, you need two layers of deck mud. A sloped layer underneath the membrane, and another layer on top of the sloped membrane. The first or bottom layer will result in a sloped membrane. The second layer on top of the membrane is for tiling upon.

Typically I'll wrap the curb in lathe prior to doing the second layer of mud, then when the second layer of deck mud is packed in place it locks the lathe in place without having to use fasteners.

When you peek inside your curb, hopefully you'll see crumbling deck mud behind the tile. If your curb tile is thinsetted to cement board, that could indicate a problem, as the only way to attach cement board to the curb is with fasteners.

Your tile guy should have a moisture meter, that can be used to see what the moisture content is of the wood in the curb.

One other thing to ask about is if the pan membrane was flood tested. It should have been done right after the membrane was in place and prior to the second layer of deck mud being placed on top of the membrane. The flood test can indicate problems at the clamping drain, at any seams, or from any punctures from errant sharp objects, etc.

Thanks for all this information, mongoct. We have decided to hire another contractor to look at the bathroom before we call back the contractor who did the work. (The contractor we are hiring is actually the same person who recommended the contractor we used).He will be coming over on Thursday.

I'll print out this thread so he can see what we've been discussing. I will definitely be taking off some time from work (along with my husband) to see what both contractors say and to see what's under the tile on the curb.