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Unread 10-18-2020, 11:32 AM   #1
larrylv
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Floor prep for Ditra

We are getting into a master bathroom remodel, and this time we have a contractor working on it. The bathroom floor will be Ditra over a concrete slab. Prior to demo, the floor was linoleum. And, while the main covering was removed, most of the floor still has some of the linoleum attached. It is the grey, fibrous, "cardboardy" stuff in the picture. Prior to installing the Ditra and tile, the floor will also need some leveling. I want to make sure the contractor handles the prep properly. How should this be done?
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Unread 10-18-2020, 02:00 PM   #2
cx
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Welcome back, Larry.

Your tiles don't give a rat's patooti whether your floor is level, they care only that it's flat. The larger the tiles, the more they care.

You need to reduce that surface to clean, water absorbent concrete before installing the Ditra.

Your contractor should already know both those things and be taking care of them.

My opinion; worth price charged.
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Last edited by cx; 10-30-2020 at 12:13 PM. Reason: typo
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Unread 10-18-2020, 02:29 PM   #3
jadnashua
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ONce they clean it off, a simple test is to pour a little water on it...if it beads up, more prep is required, if it gets absorbed, it should be okay. Do not let them use chemical cleaners as that can force contaminants into the concrete that then may require grinding it off.
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Unread 10-18-2020, 03:20 PM   #4
larrylv
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I appreciate the info. That is kind of what I thought, but useful to have it confirmed. One thing I have learned from this forum is to never make too many presumptions about contractors. And better to address an issue before the work is done. It would not be difficult to imagine somebody saying that Ditra is an uncoupling membrane, so who cares about the surface prep . . .
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Unread 10-18-2020, 04:08 PM   #5
jadnashua
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Ditra was designed to emulate the sand or mud beds used underneath tile in large areas like cathedrals (and some smaller buildings) over the centuries...it makes the tile more like a floating floor that can move independently of whatever is beneath. An unbonded mud bed is a similar thing - the whole thing can move independently of what's beneath it. We do not have an agreed upon standard to test its viability other than empirical. WHen used as directed for the situations stated, IMHO, it works. Setting a standard to verify that has been a bone of contention in the industry from what I've heard. An uncoupling membrane does not have a standard in the industry, so is an ongoing argument between some parties. The thinset on Ditra is not attached to it other than by mechanical means (the dovetail pockets)...an uncoupling membrane, the tile is bonded to it, and the uncoupling membrane is bonded to the surface, and it can stretch to absorb the movement (but not as much or in the same manner as Ditra). So, it gets messy. It's not an apples to apples comparison, thus, the standards ambiguity.
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Last edited by jadnashua; 10-18-2020 at 05:16 PM. Reason: fixed a typo omission
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Unread 10-30-2020, 12:00 PM   #6
larrylv
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edge of Kerdi Board

I need recommendations on how to handle the edge of a piece of Kerdi Board. This is in the entry area of a large shower and is not near the water spray area. As shown in the picture, the Kerdi Board comes up to the end of the wall (and the Kerdi Board will be covered with the tile). The end of the wall is plain drywall and the intention was to keep it that way. It looks like Schluter only makes corner profiles to for situations where both walls are tile. Is there a good way to address this where the tile is on only one side?
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Unread 10-30-2020, 01:10 PM   #7
redlude97
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Are you trying to cover the edge of the kerdiboard with drywall mud? You could use kerdiband overlapped onto the wall or a vinyl cornerbead overlapped onto the kerdi sheet. Then use a schluter jolly trim to cover the end of the tile and then mud the transition feathered into the drywall. They make a special corner bead with a tear away edge for these types of transitions but it's hard to find.
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Unread 10-30-2020, 01:20 PM   #8
larrylv
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It sounds like that corner bead could be a viable solution. The area is not finished yet, so we do have some options. Our first thought did include the Schluter profile on the edge of the tile, but not sure about drywall mud over the edge on the Kerdi Board.
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Unread 10-30-2020, 01:31 PM   #9
redlude97
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I'd cut back the kerdi like 1/4" and pre fill with a setting mud or even thinset. You could use all purpose but it might shrink/crack
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Unread 10-30-2020, 04:51 PM   #10
pls
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I ran the drywall past the Kerdi board, opposite of what you show and then I ran a vertical strip of kerdi band that was just to the outside edge. This effectively tied the corner together. I then used a Profile that is flush with outside wall. This is what Schluter rep recommended. In post 23 of the below thread are some pictures of what I did.
https://www.johnbridge.com/vbulletin...7s+hall&page=2
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