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Unread 05-11-2021, 12:23 PM   #1
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Kerdi Curbless thickness/transition question

Doing some planning for a curbless shower with the Kerdi system.

The Kerdi Neo-Angle Shower pan is 1 - 1/32" thick.

I was going to do a recessed install for this shower pan with 3/4" plywood for support. Obviously, the thickness of this area before any tiling would be 1 -1/32".

Then for the rest of the flooring I was going to do 23/32" OSB + 3/8" Plywood + 1/8" DITRA -on top of the floor joists. However, this gives me thickness of 1 - 7/32"

Will there be a problem with the transition from 1 - 7/32" floor thickness to 1 - 1/32"? The shower pan area would be lower than the bath floor by 3/16" and I wasn't sure if that can be feathered out with a Kerdi Band and thinsets?

Or would it better to cut a notch in the flooring joists and make it so that both areas line up evenly?

Thanks for any help you can offer.
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Unread 05-11-2021, 03:46 PM   #2
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The installation of the foam shower tray required installation of thinset between the substrate and the foam. That will take up some space. With a little bit of practice and the right trowel you can dial that in.

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Unread 05-12-2021, 10:04 AM   #3
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I am getting ready to grout a walk in shower so I have had to deal with the same issues as you. I spent a lot of time worrying and thinking about the transition. I will give you something else to worry about. In the previous bathroom I used 3/8 plywood under ditra. Proper spacing on screws etc and 2 days after applying the Ditra I noticed buckling in the surface. The plywood buckled in places between the rows of screws. I will never use 3/8 in again.

You are going to sister the existing floor joists and put plywood between the existing floor joists. Nothing says they have to be flush with the existing ones. What if the were a bit higher and you put shims on top of the existing joists to fill in the gap. I did not think of this until it was too late. When I put kerdi band on the joint between the tray and Ditra I put some extra mortar on the tray right at the seam which smoothed out the transition some. I then put on a extra band on kerdi on the tray right at the seam to build it up a bit. You also have to account for the differences in tile between the bathroom floor and shower floor. A 2x2 tile is going to have less mortar under it than a 12x24 tile.

I am still looking for the Schluter video on how use their shower trays when everything does not match up exactly
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Unread 05-14-2021, 10:55 AM   #4
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I had a very similar issue where the pan was slightly below and not flush with the subfloor. I called schluter and the customer service rep told me they actually support putting ditra under the shower pan simply for build up purposes. If it's necessary, you can do that.

If your subfloor is not flush with your shower pan, it won't be flush if you thinset the shower pan and thinset the ditra on the subfloor.
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