No Pre-Pan?...Is this right? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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11-25-2009, 03:02 PM

I have a contractor coming tomorrow that said he will make the shower mud pan for me. During my research, the only instructions and videos I saw mentions creating a sloped pre-pan (with the same mixture, usually a day before). However this particular contractor stated he'd lay the shower membrane directly on the plywood floor meaning no tar paper and no pre-pan. Is this the correct thing to do? I've included a pic for reference. I'm in a condo and don't want to leak down to the folks below me. Thanks.

Great board btw.

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Brad Denny
11-25-2009, 03:11 PM
Dexter, you definitely need the preslope. Here is an all inclusive thread combining the information you could print out to your contractor to prove your point.

Welcome to the forum BTW!

11-25-2009, 03:16 PM
Hi Dexter, welcome to the forum. :)

Many contractors and even professional plumbers don't know that the pan liner is supposed to be sloped towards the drain. Some inspectors don't know better either. You will hear "I've been doing it this way for xx years and have never had a problem."

Well, think about it for a sec and you'll realize that an unsloped pan may not leak, but it won't force water towards the drain either. That means the mud bed will be saturated and stagnant, which leads to mold and stink.

It also causes water to be wicked up the cement board, which is fastened to woods studs, which means the studs will get wet and mold.

In a sloped system, there is pressure towards the drain. This means the outer edges dry first, which is a very good thing. Water will go into the mud bed, but it is flushed towards the drain keeping things from becoming stagnant. This is called a "water in - water out" system, and it works.

I would point him to the instructions provided by the liner manufacturers, Oatey (, and Noble (

Both say that the liner must be sloped. :)

11-25-2009, 03:28 PM
Exactly why I come to this board. Excellent information so quickly. I will insist on the membrane being sloped.

One other question, as you can see the drain has a wide hole around it. I guess it's as simple as laying another piece of plywood over the existing right?

I'm about to go to home depot for framing materials but wondered if I need to get more ply.

11-25-2009, 03:40 PM
I'd want to patch in a piece of plywood, flush with the existing plywood so the drain is properly supported. I'd glue and screw some 2x under that grand canyon sized hole so that the patch can be screwed down to the new 2x. You want it solid.

11-25-2009, 03:51 PM
Forgive me DaveM, but I wouldn't know how to "patch". Novice here. I only know there was a fiberglass shower in this space before I ripped it out. The drain leads somewhere throughout the condo structure. I thought laying down a new piece of plywood over the existing would make things sturdy.

11-25-2009, 04:17 PM
Dexter, you might want to post a closer pitcher of that drain. We want to make sure you have the right drain in place. :)

11-25-2009, 04:26 PM
that doesn't look like a clamping drain to me.
I dont see the separation on the outside ring.

11-25-2009, 04:44 PM
Here you go. Moves pretty freely to me.

11-25-2009, 04:45 PM
As the others have said, you want a pre-slope. I am tearing out a shower right now with no pre-slope. Water was standing in the pan as I took out the mud. The weep holes in the clamping drain were higher than the water standing in the pan. This shower is 4 years old.

11-25-2009, 04:49 PM
That drain still does not look like the right one. I am willing that is the same drain that the fiberglass shower attached too. Here is a pic of the clamping drain.

11-25-2009, 04:55 PM
You may want to read through the link above for yourself so you can keep an eye on the installer, keep him honest. Replace that drain for sure. MUST be a 2 piece clamping drain, the liner goes between the 2 pieces. That drain is a 1 piece and there is no way to attach the liner to it.

Good luck and welcome to the forums!

11-25-2009, 05:09 PM are on point! Sorry for the confusion. Yes, we have not cut the drain off yet. It was a part of the fiberglass shower. I plan on replacing it with one like you mentioned.

11-25-2009, 05:10 PM
Btw, YUCK! on the shower floor. A pre-slope is def. needed.

11-25-2009, 05:31 PM
this might help..