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Kerdi valve seal installation question

Posted by toolbabe (My Page) on
Tue, Feb 23, 10 at 10:50

Hi there, me again...

We have opted to have a Kerdi membrane installed as part of our bathroom reno. The question I have concerns the shower mixing valve seals. Apparently, Kerdi seals are only available in two sizes: one for the pipes and one for mixing valve seals which is a 4 1/2" round thing.

Our Riobel Retro mixing valve have oval face plates which are 4 3/4" at their narrowest.

Me thought, no problem, the face plate will fit nicely over the round Kerdi valve seal. And the lip of the seal will not protrude beyond the side of the tile. We're good.

Tile pro nixed that idea and although he did use the pipe seals, he went ahead without installing the Kerdi valve seals. Said he'd walk if I insisted on them because he would be doing me a disservice by installing them. He explained that the valve seals are overkill and that they would get in the way of laying the tiles properly. Said he'd run a proper bead of silicon around the outside perimeter of the face plate to make the seal. Gasp....

Doesn't that defeat the purpose of having a Kerdi system installed in the first place?

Follow-Up Postings:

RE: Kerdi valve seal installation question

IMO, perfectly acceptable. A lot of plates ship with a foam strip 3/4 or so of the way around the inside of the plate. Bottom is open to drain anything that gets past the inner ring. I used the kerdi ring because it fit my plate but the plate had the compressible foam so it was probably redundant.

RE: Kerdi valve seal installation question

I agree. I've done quite a few Kerdi Showers, including several steam showers, and I've yet to use any kind of valve seal.

RE: Kerdi valve seal installation question

Thank you for the reassurance, Jeffrow,

The face plates did come with strips of foam, but our tile man ripped them out saying they only become a source or mildew as they fill up with wet debris. Does that make sense to you?

RE: Kerdi valve seal installation question

I don't see how sealing the valve with Kerdi will affect laying the tile. All of the Kerdi behind the valve plate doesn't necessarily have to be covered with tile if that's the guy's objection. I use Kerdi-Fix or equivalent to seal the membrane to the valve.

In regular showers I don't seal the Kerdi to the the valve. It's really not required and doesn't improve things water-wise.

In steam showers I do.

I never caulk the escutcheon or valve cover plate to the tile. If for some reason you wanted to, don't caulk it at the 6 o'clock position. Leave that open for water drainage, just in case.

The foam strips on the back of the escutcheon plates should have been left intact. They prevent water that runs down the valve wall from getting behind the escutcheon plate or valve cover. If they get behind the plate then the water could get into the wall through the valve hole.

More technique than procedure I suppose, but that's how I do things.

RE: Kerdi valve seal installation question

Thanks Mongo,

I was hoping you'd field this question. :-)

Oh well, more experience for the next project. I'll replace the missing tack foam with a loop of grey insulation tubing, the fine one, and yes, with a little gap at the bottom for the water to run through.

RE: Kerdi valve seal installation question


In a steam shower, when you seal the Kerdi to the valve, are you using Kerdi-Fix to make a watertight seal around the body of the valve?

Does the plaster guard come off or do you glue the Kerdi to it?

I've heard before about leaving the bottom of the escutcheon unsealed, but doesn't that allow steam to penetrate in a steam shower?

RE: Kerdi valve seal installation question

1) In a steam shower I want to do the best I can to prevent vapor from getting into the wall through the valve opening. While it depends on the valve, when Kerdi-ing I'll try to slice the Kerdi and adhere it to the valve body with Kerdi-Fix. Neatly as possible, without gunking up the valve or it's threadings, or adjustment screws, or...

2) Plaster Guard, it depends on the valve. Some valve bodies come with a plaster guard that is simply meant to protect the valve during installation. It gets removed during the finishing phase. Other valves have plaster guards that remain in place after the work is complete. Some are hybrid guards/mounting plates.

If I can use the guard to my advantage, I keep it. If it's in the way, then out it goes. It all depends on the end goal, which for me in a steam shower is sealing the opening without compromising the valve. There's often not a "one size fits all" solution. Just detail things as you're able.

3) Unsealed escutcheon. I might not have been clear in my previous post, but I install the escutcheon just like the installation instructions say. In a regular shower the hole in the wall behind the escutcheon can remain open. In a steam shower I seal the opening behind the escutcheon.

All the above is a "my way" type of thing. It's not the only way for sure.

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