I have a contractor installing a shower pan (mud pan). I have serious doubts about how this is being done. The shower is a walk-in, and being built on a concrete slab in a basement (the basement has never had any moisture problems).

My concern is that the contractor states that if a preslope is added under the liner, then the next layer of the mud pan (placed on top of the liner) will be too thin near the drain. I've provided some pictures here, since it is so much easier to see the concern:

pictures of the liner install

The contractor indicates that if the liner is placed directly on the concrete, then the liner will be firmly held to the slab and there will be a deeper depth of material resting on the liner to hold it in place.

My concern is, how then can water that reaches the liner drain to the center drain (it would then be the highest point in the floor). Also, with the way the liner is installed now, it seems there would be an air-gap all around the drain with a potential for the liner to stretch at the drain and possibly create a tear.

you could raise the drain probably an inch? and the curb if need be.I see from the photos your drain is recessed all the way.

Hi Mark,

Your concern is right on. Within a few months of using that shower you will have moisture trapped and that is NOT a good thing. To do the job right you need a preslope or change to a Kerdi Drain system. I don't understand your concern about air gap, there won't be any air gaps.

The contractor perhaps has never done a preslope? The preslope is bonded to the slab and only needs to be about 3/8" thick at the drain. From there it'll slope up to about 3/4" or so to the walls judging by the size of the shower. (1/4" per lin. ft. as you know). Over that you install the membrane then the finish mortar bed will be from maybe 1"-1 1/4"(?) at the drain to 1 1/2"- 1 1/34" or whatever at the perimeter.

I also don't like the way your curb is membraned, and how are you gonna waterproof the kneewall?

Jaz

Hi Mark

The inspectors in Fairfax County aren't too terribly picky about shower pans, but even they aren't going to let that one pass (assuming you are permitting this job).

There really isn't anything good to say about that liner, and I would insist on it being taken out and redone to the specs in the TCA handbook.

Jaz is right .... you either need a slope under the liner or a waterproof membrane like Kerdi to direct water straight to the drain.
If he's using the correct drain assembly ... the trap will adjust to allow for almost 1-1/4" of mortar bed at the drain.
All your concerns are ones you should confront your contractor with so that he's aware you're not going to settle for an improper shower pan.

Thank you Jaz,

Some elaboration:

I don't understand your concern about air gap, there won't be any air gaps.

-Jaz, I am referring to the area under the membrame at the drain ring, if there is nothing filling the void, then there will be an air gap where the membrane transitions from the floor and rises to meet the drain ring. I doubt that the fill material will provide enough compression to force the membrain tight to the drain. Either way, it is clear that this particular install is not satisfactory.

I also don't like the way your curb is membraned, and how are you gonna waterproof the kneewall?

Yeah, I'm not so fond of that either. I think the plan is to put Durarock or green board on the knee wall inside the shower and on facing parts of wood. Outside the shower will be drywall finish.

A good source for purchasing a Kerdi-drain would be welcomed (I could just get one for the contractor to make his life easier).

Yep, it's permitted and the inspector has been by once already.

Don't even think about greenboard for any part of your shower. (Pure garbage)

Stick with cement board for all the tile backer.

Hope your liner issues get fixed up.

If the problem is that the male end of the drain piece isn't long enough,then take it to a good plumbing shop and they can glue on another section of threaded ABS or PVC.

Mark

Did the Fx County inspector let that pass?