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06-29-2008, 10:41 AM
I am seeing a lot of conflicting information on how to pour a concrete shower base. I have a irregular shaped walk-in shower that is roughly 5'x7' (including the walk-in area). The drain is already installed and I have water-resistant sheetrock on the walls.

The biggest conflicting question is whether I need to pre-slope the base before installing the liner or if I can just install the liner in on the flat sub-floor.

I am a bit worried about leaks since the area is irregularly shaped and I will have to seam the liner. If I place the liner on the flat subfloor, then I will make a curb near the step-in that will go beneath the concrete and act as a water dam.

But I am not sure if I should slope the floor before installing the liner then add more concrete on top.


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06-29-2008, 10:49 AM
You need to put the preslope in before the liner..

If you put the liner in flat on your subfloor, when water penetrates through the tile,grout,mudbed.. then it will sit flat on your liner and not drain properly.

The preslope, prior to the liner being installed, is one of the most important thing to have for a long lasting shower. :)

You mention "Water Resistant Sheetrock" what would this been? Denshield? Greenboard?

06-29-2008, 10:59 AM
when water penetrates through the tile,grout,mudbed..

Notice that kurgon said "when " and not "if". Water will get to the liner, anyone that has ever ripped out a shower stall knows this.

06-29-2008, 11:05 AM
Thanks for the help. I was afraid of that. This will about double the amount of work involved.

Since I already have a drain and water-resist drywall installed, my understanding of the steps required are:
1) Add curb near step-in (concrete or bricks).
2) Pour concrete base directly on subfloor to slope floor 1/4" per linear foot.
3) Wrap in 15# felt.
4) Add 4mm liner using pvc adhesive for seams run up the walls at least 9" and over the curb.
5) Cut liner at drain and clamp bottom of drain onto liner and seal with (silicone? or pvc adhesive?)
6) add pea gravel around drain weep holes so they are not plugged by concrete.
7) Pour top concrete layer with laytex additive (how thick though? 1"=2"?)
8) Install felt and concrete backer board on walls with felt overlapping the liner and making sure to not puncture the liner.
I have read that I should leave a 1"-2" gap above the mud base so water is not siphoned up the back of the backer board and to fill this gap with thinset. Is this true?
9) allow to dry 24hrs
10) start tiling.

Steve in PA
06-29-2008, 11:08 AM
A better option would be to do the full mud bed over the flat sub floor w/felt and wire lath. nix the liner and go with the kerdi system. the kerdi will really waterproof your non waterproof moisture resistant drywall.

06-29-2008, 11:28 AM
Sean, look for the Shower Construction thread in the Liberry. There's a lot of good information in there along with some good pictures from Harry Dunbar of the steps involved in building a pre-slope.

chuck stevenson
06-29-2008, 11:29 AM

I agree with Steve(Kilroy) With the kerdi you eliminate the backerboard. Kerdi is 100% waterproof when properly installed.

I think your 2' shower entrance is on the small side.

06-29-2008, 12:19 PM
I agree with using the Kerdi. I believe it is the most foolproof way for a DIYer to achieve a waterproof, leakproof shower. You definitely don't want drywall of any kind behind your tile unless you waterproof it with something like Kerdi.

06-29-2008, 05:01 PM
thanks for the input. Looks like I am going with the Kerdi system. :)

BTW, the drawing was just rough, the opening is really about 2'5".

Looks like I will be starting with the kids bathroom while I wait for the kerdi materials to arrive.

This makes me alot more confident since I can pour the base all at once and feel better about the niche. I will let you know how it goes.

chuck stevenson
06-29-2008, 06:18 PM

The base is not "poured" it is placed.

Here is a link for Deck Mud (

You can download JB's "The Kerdi Shower Book" and save yourself time and money.

06-29-2008, 07:35 PM
Sean, welcome to the forum. :)

Like Chuck said, get the Kerdi ebook, read up on mud bed installs in the Liberry and get all the info you need there, and then here, to make this a very successful project.

Mud beds are fun and very rewarding. Using the Kerdi system is pretty easy as well and the folks here will be more than happy to help you through any questions or confusion. And there may be a little of both. ;)

Looking forward to following your progress and hoping we'll get some pitchers along the way. :)

06-29-2008, 08:20 PM
This thread is very useful! I am having the same experience about conflicting information on the install of the shower pan.

Anybody have any experience with the Canadian "Dix systems" for presloping?
There is a url but I can seem to include it here.

Dan in Texas
06-29-2008, 09:50 PM
I did not use the Dix system but I did use the perfect pitch system from Mark E. Industries. If you go with Perfect Pitch make sure you get enough sticks to have the ends less than 2 feet apart. They also sell extensions for the sticks and you will need some if I'm not mistaken. The sticks are about three feet long before the extensions. If I was doing mud decks all the time I think I would get good enough not to need them but doing one and wanting to be sure it was right I went with it. Dan

06-30-2008, 01:58 PM
One of my replies got lost it seems...

I bought the ebook and am most of the way through it, but one question:

Can I use the standard drain that was installed by the plumbers or do I have to use the Kerdi-compatible drain?

06-30-2008, 02:12 PM
You need the Kerdi drain. It is possible to clamp the Kerdi under the clamping ring of a regular shower drain, but you'd have to caulk it to be water tight, and then you'd loose the weepholes in the drain and you'd have to put 1 1/2" of deck mud over the Kerdi, thus eliminating any benefit from using Kerdi in the first place.