Insist on the Kerdi drain. Kerdi over what you have there won't do a damn thing. In addition, I'd bet a paycheck that the liner underneath is sitting on a flat subfloor. Tell this guy if he doesn't want to do it right, you'll get someone who will.

The liner is installed over some type of wooden underlayment that was secured to the plywood subfloor. Yep, I believe it's flat underneath. What problem does this cause and how should it be corrected?

A Kerdi shower is a complete system and includes the drain. I would send these hacks packing!

There should be a "pre-slope", then the liner, than the final mud bed, then the tile. Without a pre-slope, the water that hits the liner will not flow to the drain properly and will pool in corners or low spots, yuk, mold and mildew and smells will develop. And the picture of the liner you show is built wrong...what is the deal with the nails so low, about an inch off the top surface of the bed? And there is no wood backing between the studs...looks like the liner is flapping in the breeze between the studs?

The lack of pre-slope is wide spread...I actually saw episodes on This Old House with installers not using a pre-slope.

I'm told the Kerdi will be applied to the surface of the mud bed which is sloped. The existing drain will be removed and replaced with a kerdi drain. Is this proper or does the wood underlayment the mud bed is built on need to be sloped as well?

I'm not hopeful that this will turn out right. You are too timid and you haven't cottoned on to what was done wrong so far.

Preslope is required by Code. Preslope is a built slope onto which one applies the membrane (there are a hundred options for membrane, so Kerdi is only one, and not the solution "per se".)

When a membrane has been installed flat, it will cause big problems later.
When an installer doesn't know this, it is a serious indication that they will not do the right thing later ALSO.

Membranes, in general, of all kinds (not just shower floor membranes), must not be doubled up with a space between them.

If anyone tells you they will now leave the faulty membrane as is and now begin to install "the right membrane" on a slope, they are guaranteeing your installation will fail. Also, they are confirming what I wrote above, i.e. that they will not be able to do the right thing later. Say no to the idea that two membranes are better than one.

hope this helps. You have more than one problem.

fish,

The membrane "as is" is no good due to the fasteners that have been driven through it about an inch above the existing mud. If it is indeed installed on a flat subfloor, then that's a no-go too. Both of those are not just poor techique, they are code violations.

Moving on...

If you want Kerdi you want a Kerdi drain, too. Kerdi membrane on the walls and floor is not compatable with a non-Kerdi drain.

A CPE or CPVC membrane in the floor is not compatable with a Kerdi drain.

So the installer giving you the CPE membrane with the intention of using Kerdi? It's doing you no good at all. They don't work together, there's no synergy. It's not 1+1=3, it's 1+1=0. It's not a double bonus, it's a double negative.

If he can break out the mud around the existing drain, remove it and install a Kerdi drain at the proper elevation, then feather in new deck mud to match the flange of the Kerdi drain to the slope of the existing mud, then bravo.

But do realize that unlike the 2-part clamping drain that you have now, which is height adjustable after is is installed, there is no vertical adjustment to the Kerdi flange after it is installed. So if your installer just wants to patch a Kerdi drain in place, he has to be pretty darn precise when he installs the drain. It's a "one and done" shot to get the drain at the correct elevation and to get it level. I highlight "level" because the flange on the kerdi drain has a large diameter, it's like a frisbee. It needs to be spot-on level and at the proper elevation for your floor to drain properly.

With the Kerdi system there is only one slope under the Kerdi and no mud bed above. I agree that 2 membranes is asking for trouble. This contractor obviously didn't read or understand the Kerdi instructions. My guess is that he didn't read them at all.

Two membranes is asking for trouble.

Because any combination of two membranes (with a little space between them) aggravates the mold and rot problem instead of solving the problem. They cancel each other out.

It's not because it's Kerdi. Any two membranes of any kind, anywhere. Housewrap vapor wrap, air barrier, etc, on walls ceilings roofs etc.

"Two membranes is asking for trouble." In the thermal envelope of the house that's true. But not any two "membranes". Two vapor barriers is not permitted. In heating climates a housewrap on the exterior and a vapor barrier on the interior are common and preferred.

Not necessarily a problem on a shower floor. The CPE will be destroyed around the drain when the new drain is installed.

And most properly constructed shower floors have "two membranes". Installers use a slip sheet (usually 6-mil plastic sheeting) between the subfloor and the drypack preslope. That's membrane #1. Then either the CPR membrane withing the mud base or Kerdi on top.

In this guys case the CPE that runs up the walls should be cut just above the layer of deck mud.

Can this installation be repaired by inserting a Kerdi drain into the deck mud? Yes, if the installer is a competent technician. If he's not, then sure, demo it and start over and do it by the book.

I understand what David's talking about, and from his frame of reference, he's right. IF the Chloroloy were to be left in place and intact, then yes, it WOULD create the infamous "moisture sandwich", which no matter whether it's a vertical or horizontal surface, would be a big problem.

Hello again,

I had a discussion with the installer a few days ago and let him know I want everything installed per the manufacturers instructions. He assured me it would not be a problem from this point forward.

I contacted Schluter, and as some of you guys mentioned, the rubber liner will be fine if left in place as long as the drain is replaced.

The installer has decided to attempt to replace the drain with the kerdi drain. He seems confident that he can do it.

I'm going to let him try and if its not proper it will be gutted.

We're also using kerdi on two bathtub surrounds. I checked on the progress today and the kerdi was installed on the surrounds using the multipurpose laticrete thinset pictured. I have a sinking feeling it's a modified thinset. Can anyone confirm? Will it need to be redone?

If it needs to be redone, this crew is gone.

This is turning into a real headache.

Thanks for all of the guidance.

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If you look on the label on the left in the picture, you'll see where it says "A polymer fortified adhesive for interior and exterior installations" That means modified. However, I don't see that it causes a real problem. It just means that before you use it, you need to let about a week or two go by from the time the Kerdi went up.