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Unread 05-06-2021, 11:20 AM   #1
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Tile floor and Kerdi/ditra advice

Hello---new to the forum and would appreciate any advice/guidance on the following.

Project- Laundry room floor

Room is 5'x8'

Subfloor is 3/4" T&G plywood supported by 2x10 joists (in good condition) 16" OC spanning 13.5' (appears to exceed minimum deflection requirements for ceramic tile).

Currently the washing machine sits in a large hard plastic washing machine drain pan (with a 3" drain in the center)

Replace existing linoleum with ceramic brick tile (approx. 9"x3" tile).

Plan is to:
-Ensure floor is flat (or take steps to flatten within required tolerances.
-Remove/dispose of large plastic drain pan (just to big and bulky and does not fit the new plan to effectively enclose (sides and top) of new washer/dryer
-Build a platform directly on the plywood subfloor for Washer and Dryer to sit on that would be 4" above finished floor height. The platform would also have a 2" tall lip all around the three sides (back is a wall).
-Install Ditra over plywood subfloor (around the washer/dryer platform then tile (using schluter instructions/materials).
-I would like to take steps to limit the extent of any water damage in the event of a washing machine or hose leak

I have considered and ruled out using a drain pan and have been considering taking steps to waterproof the area/platform, that the washing machine would sit on, so that any leak would be contained and funnel to the drain in floor (understanding that as it would not be sloped it would still be effective in the event of any significant leak---the old --"an once of prevention is worth....").

I would like to use something like the kerdi membrane to waterproof (or liquid redgard) ---but dont want to have to tile over it. I would ultimately put some plywood over the area where the washing machine feet would be to prevent any excess wear on the kerdi.

1) Any issues with using the ceramic brick tile --given the floor characteristics and use of ditra?
1) As it relates to the area i would like to waterproof under washing machine---should I put some type of finish or material over the kerdi/redgard that would protect it (thinset, mortar, etc..). I know Schluter would always indicate it should be tiled.
2) As an alternative to kerdi--should I consider using something like an Oatly PVC liner

Thank you for your help
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Unread 05-06-2021, 12:13 PM   #2
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Welcome, Ben,

My first questions - where does the existing 3" drain lead to, daylight?

As for laying down Ditra as a water proof layer on the main floor, the week link will be were the floor meets the walls and the doorway. Unless you seal the Ditra to the walls and to the raised platform, and build a curb at the doorway, any significant amount of water is going to exit via one of those paths. I assume you intend to extend the drain up to the new 4" high platform.

As for the platform, Kerdi is not a wear surface, and even if it were there's no way I'd put a washer and dryer on it. The point loads from, and the vibrations transmitted through the small diameter feet would tear it up. Same for a PVC liner. Any liquid membrane would fare much worse.
If I recall correctly my memory is excellent, but my ability to access it is intermittent.
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Unread 05-06-2021, 02:25 PM   #3
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Thank you for the quick response.

As it relates to your first question----it is plumbed (with a p trap) to other internal drains. I understand the trap needs continual priming.

To clarify--- i am using ditra on the main part of the floor as an uncoupling membrane over 3/4 plywood subfloor and not as an attempt at waterproofing that section.

As it relates to the 4" platform---i do intend to extend drain up to it and the platform will have a lip (curb) to contain/direct water down to center drain. I would plan on using kerdi up on the lip/curb and along the back wall.

I agree that Kerdi or a membrane untreated/covered would not be good for direct contact with a vibrating washing machine. That is the essence of my questions----could i apply a skim coat of thinset or mortar over it to protect and then even put a piece of plywood (sacrificial if it gets wet) over the now skimmed kerdi (so washing machine sits on plywood or some other hard surface). Hope that makes sense.

Thanks again for your insight and advice.
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Unread 05-06-2021, 03:00 PM   #4
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Tiling membranes are designed specifically to be covered with a tile installation. There is no way around that.
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Unread 05-06-2021, 04:09 PM   #5
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Some membranes designed for roofs and decks are designed for things like pavers or a floating wooden structure to sit on top of them.

If you make your platform stiff enough, you could use Ditra and then tile it. Use KerdiBand, or strips of Kerdi over the seams to waterproof it.

You could probably use Kerdiboard by itself if you then tiled over it as your platform, waterproofing, and tile substrate. Two layers of the 2" stuff, with a channel for your drain pipe wouldn't have any deflection issues once you tiled it and things had cured. They use that type of foam on bridge ramps instead of compacting stone and gravel...spread the point load out with a suitable tile, and it's robust.
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 05-06-2021, 05:52 PM   #6
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thank you both for the insight and response.

Good suggestions.

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