"Could the cracking of the grout be from moisture from the opening of the concrete floor under the shower? i" You pretty much hit it on the head there in that it is moisture related. For the most part, it could be from one of three things: 1) It could be moisture or moisture vapor coming though the unplugged hole, and wicking outwards to the curb. But if that was the case, in terms of there being significant moisture, you'd probably see signs of water presence or water damage at the base of the curb. 2) It could be the wood curb simply wicking moisture through the slab below. The thing it, as best as I can read the photos, it appears that the majority of the swelling is on the top of your curb. The tile on the outside curb facing could have the bottom edge locked in place by the floor tile, in that case it could be the floor tile that is preventing the bottom edge of the curb tile from blowing out. But to me it looks like the curb tile sits on top of the floor tile, so if the bottom of the curb tile wanted to blow out, it would be free to move. Correct? Incorrect? Based on that assumption? I'd guess that: 3) In the first two photos, it looks like there is a metal track or trim on top of the curb. If that track/trim has been fastened through into the top of the curb, it's possible that moisture is getting to the curb through the fastener holes. The top of the wood curb got wet, then expanded, and it's that expansion that is blowing the curb apart. I don't know how the membrane was detailed at the curb. It should be wrapped up the inside face, over the top of the curb, and stapled on the outside face of the curb. Any fasteners through the top of the curb could have penetrated the membrane and allow moisture to get to the wood. I've seen a lot of curbs where the membrane never completely made it over the top of the curb. In that case, it could be as simple as water intrusion through the grout lines on top of the curb. Again, that's based upon my assumption (cough, cough) that the floor tile outside the shower is not locking the curb tile in place and the bottom edge of the curb tile is free to move if it had to.

Bill, Any thoughts on whether Hydroban left exposed on the top of the curb will work for a couple of years? If exposed Hydroban won't work, could I get away with installing a cheap solid piece using silicone or something like silicone that would make removal easier? More than pulling off the hydroban, I'm worried that large chunks of thinset and maybe even the vertical portions of the curb I want to keep will come out at the time of removal.

Thank you for your input! I just asked our GC about it, and he said that we can't do it since the plumbing won't work out. If we put the shower head across from the door, it will be very hard to turn the shower on. We can't put it on the outside wall, so we are limited to the wall next to the toilet. He suggested keeping it as is and using a glass door instead of a curtain for a more "finished" look. Does this seem to make sense? Thank you again! I did not realize our idea would not be feasible. :-( Sara

If I'm understanding your post correctly...it depends on the construction/design of the pan. If the pan can't bear the weight of the wall framed right on top of it, probably the easiest would be to build a 2x6 wall and notch out the bottom of one side of the studs to go over the curb. Example...let's say your curb is 4" wide and 3" high. Think of the stud standing vertically. You'd want the notch to be tall enough to clear the curb height, say 3-1/8" to 3-1/4". You'd want the notch to be deep enough to cover most of the curb, but not so deep that the stud is too fragile after it is notched. So for this example make the notch 2-3/4" deep, leaving 2-3/4" of the 5-1/2" width of the 2x6 uncut. A 2-3/4" deep notch will cover 2-3/4" of the 4" of curb width, leaving 1-1/4" of the curb exposed. In the drawing below, think of the "x" as the stud and the "o" as the pan. You can see how the stud is notched out to accept the pan. The "z" is the sole plate for the wall. You'll have two sole plates. One at the bottom of the wall that will sit on the bathroom floor, one at the bottom of the notch that will sit just above the top of the pan's curb. "c" is the cement board and "t" is the tile. xxxxxxct xxxxxxct xxxxxxct xxxxxxct xxxzzzct xxxoooooo xxxoooooo xxxooooooooooooooooooooooo zzzooooooooooooooooooooooo When you add the cement board and tile to the inside face of the wall, it'll build it out a bit, but a bit of the edge of the curb will remain visible. How much depends on the style of the curb, if the edge is closer to square, or if it has a generous radius, etc. If you use 6-mil poly in that wall, seal the bottom edge of it to the top of the curb. In this case, your curb is 4" thick, the notch is 2-3/4" deep, leaving 1-1/4" of curb exposed. The 1/2" of cement board, the 1/8" thickness of thinset, and the 1/4" thickness of the tile will cover another 7/8ths-inch of the curb, leaving 3/8" of the curb exposed. One other comment...if the inside edge of the curb is dead straight then all will look fine. If the inside edge of the curb waivers in and out a bit, that 3/8" of curb might go from 3/8", to 1/2", to 1/4", etc, as the curb waffles around. The more your curb waffles in and out, the more curb you need to leave exposed to compensate for the waffling. With 2x6 framing, this will be a "thick" wall. A great opportunity to use the stud bays for storage. A shower niche on the inside, or a tall "medicine cabinet" or "storage pantry" built in to the stud bays on the opposite side.