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Unread 10-23-2021, 07:59 PM   #1
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Join Date: Oct 2021
Location: Boise
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Kerdi over Redgard & Shower Drain question

I’ve watched this forum for a long time and used it to help create a master bath from scratch, and turn a bathroom that had a clawfoot bathtub into a walk-in shower (mortar bed, schluter/kerdi/ditra drain and waterproofing). Thank you all so much for your sage and honest advice!

I have a conundrum. I have a poured cement bathtub in my 1940s house that I am converting to a walk-in shower with a mosaic tile floor & 12 x 24 large format wall tiles. The tub walls are 4-5” thick & the tub floor 3-4” thick cement. I’m keeping it & have to work around it

Problem 1: The old 1 1/2” drain pipe and collar were embedded in concrete had to be cut out with a cement saw & I now have a 5” hole where the drain used to be. It sits right up against the cement wall where the water mixer value and shower head are now. I can’t use a clamping flange or a Schluter product because they’re either too wide or too thick. What would you suggest? (I’m attaching a picture, or trying!) I’ve got access from underneath the shower. (Picture attached.)

* note added after CX’s wise observation: The floor slopes in the middle (from both sides - concave) and down to the drain, so moving the drain to the center won’t help - the flanges won’t sit flat.

Problem 2: I Redgarded the cement floor after I realized I couldn’t use the Schluter drain system. When I pulled up the tile at the beginning of the project, it was attached to the cement floor with mortar, without any waterproofing at all.

Can I lay kerdi membrane over the top of the Redgard with a modified polymer mortar, and then use unmodified between the Kerdi and the tile?

* the wood is where the curbing is going to be for the walk in shower.
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Last edited by MontecoreB; 10-24-2021 at 11:38 AM. Reason: I left out information in my first post
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Unread 10-23-2021, 09:33 PM   #2
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Welcome, Bianca.

I'd recommend you use the same tile saw to cut a hole in the floor in the center of your shower footprint. Then you can install a bonding flange drain and a properly sloped floor. What waterproofing material you use for the shower receptor is up to you, but I'd recommend a sheet-type membrane. Kerdi is one such.

I'd recommend you remove the existing RedGard before placing the new sloped floor.

What is the purpose of the wood piece we see on top of the apparently cut down curb at the front of your shower?

My opinion; worth price charged.

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Unread 10-23-2021, 11:10 PM   #3
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Location: Nashua, NH
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If that galvanized piping is water or drain, I'd replace all of it while you have things open.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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Unread 10-25-2021, 06:31 PM   #4
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Short of moving the drain or removing the concrete floor, any other ideas?

Thank you, CX. Your advice is spot-on and I know yours is the best solution if possible, but given the sloping issues with the existing floor, I’m trying to work with the current floor and drain location.

I was thinking of just putting in a 2” pipe with a screw top drain (Oatey) and filling it in with concrete, with a membrane (kerdi) over the floor and into the 5” hole before I fill it. (See pix added.) I’m kind of at a loss of what to do to make sure it’s waterproof.
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