Help with shower tub.

I bought my house 5 years ago. Since the day we bought it, we knew one of the bathrooms would have to be gutted and redone. We hired a contractor friend to do the job last October. We've been happy with the results, until this past week. During a massive rain storm, my son showered, and we had a leak into the basement which was coming from the new shower stall. We didn't know if it was the bathroom, or the storm. At one point, we thought it might be the drain backing up from all the rain. My friend came to see and actually opened the wall on the outside of the shower (the hallway) to see if any water was getting behind the tile. This was done directly above the leak, but the shower had not been used in 24 hours. Nothing appeared wet, so we went on inspecting and eventually found an unglued vent pipe in the basement, and we assumed that was the problem. He agreed to come back over the weekend to redo the vent pipe (which was from the original bathroom - he never touched it).

Now.......fast forward to tonight. My son takes a shower, and it occurs to me to look in the basement, where I find new moisture, but the vent pipe is dry, so now we can rule out the vent joint being unglued. I come back upstairs, and decide to open up more of the wall, and I saw that the membrane under the shower base was holding about 2 inches of water between it, and the concrete board (basically the bottom row of tiles in the shower. It then occured to me that the big leak from Friday had to be caused by water overflowing the membrane.

The old bathroom had a plastic shower base, but the drain was centered over a joist, and whoever built it, had cut the joist. My friend repaired the joist, and to put the new drain off-center, he had to build the shower base as follows........

Plywood on the bottom. (3/4 inch)

Cement board on the walls (1/2 inch)

Rubber membrane over plywood and coming up about 8 to 10 inches over the wall.

Poured concrete over the membrane. Concrete was shaped so water drains to the middle.

Tile over the concrete, and tile over the concrete boards in the wall..

The joints where the floor meets the wall, and the walls meet each other are caulked, and everything else is non-sanded grout.

So now the question(s) are:

This membrane is not supposed to have 2 inches of water in it after someone showers, correct ?. The membrane should remain dry and only act as a barrier if something fails, like caulk, grout, drain, etc.......is that right ?. I just want to make sure I am not going to be told this is normal. Clearly, the leak came from water overflowing the membrane.

From what I listed above, does the method for building the shower look right ?. Was something missed ?

Thanks for the help. I can post pix if needed.

PS: In case the shower needs to be redone, I may want to give up on the concrete base and go back to the plastic base. Does anybody know if they make these with the drain off center ? It only needs to be off center about 4 inches to clear the joist.


From your description, the shower was not built correctly, and your pan is holding water. Water is not making it to the weep holes in the clamping drain due to lack of a preslope underneath the membrane (required by code and you do not have one), or the weep holes are clogged and water is not able to escape to the drain.

Tile, grout and caulk are not what makes your pan waterproof, the membrane is designed to do that. As water seeps through the grout lines, it should flow through the mud bed where it should reach the liner and then eventually make its way to the drain weepholes. It sounds like this is not happening with your shower.