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Old 03-15-2014, 05:42 PM   #1
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Leveller over DITRA


We installed Ditra over plywood but noticed the floor (8x4) still humps up in the middle. I'd like a perfectly flat floor before tiling - is this possible to add leveller over the installed Ditra?

Secondly, I was told to add a layer of mortar over the Ditra and let dry before tiling for best strength (filling in all the dimples)

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Old 03-15-2014, 09:55 PM   #2
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Leveller over DITRA


I've never tried a leveler over Ditra, but I think in theory it should work.

It is not true that you get best strength with 2 layers of thinset mortar. I'm not sure why anyone would think that. In general, 1 layer of anything like this is going to be stronger than 2 layers.

Having said that, the strength will be close enough that it makes no difference in practice. Any strength difference would be undetectable in this scenario. What I tend to do is put down the Ditra with thinset, and with the extra thinset, rather than throwing it out, I fill in the waffles. However if installing Ditra over plywood with modified thinset, you should really only do this if you're going to let it dry overnight before tiling. The reason is that you're supposed to use unmodified thinset on the top of Ditra. If you installed the tile with modified thinset, it wouldn't be able to dry properly, and modified thinset must dry to form top strength. Unmodified does not need to dry. But leaving it overnight to dry before installing the tile solves that problem.

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Old 03-15-2014, 10:09 PM   #3
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Leveller over DITRA


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Originally Posted by jeffnc
I've never tried a leveler over Ditra, but I think in theory it should work. It is not true that you get best strength with 2 layers of thinset mortar. I'm not sure why anyone would think that. In general, 1 layer of anything like this is going to be stronger than 2 layers. Having said that, the strength will be close enough that it makes no difference in practice. Any strength difference would be undetectable in this scenario. What I tend to do is put down the Ditra with thinset, and with the extra thinset, rather than throwing it out, I fill in the waffles. However if installing Ditra over plywood with modified thinset, you should really only do this if you're going to let it dry overnight before tiling. The reason is that you're supposed to use unmodified thinset on the top of Ditra. If you installed the tile with modified thinset, it wouldn't be able to dry properly, and modified thinset must dry to form top strength. Unmodified does not need to dry. But leaving it overnight to dry before installing the tile solves that problem.
Thanks for the reply Jeff... That makes a lot of sense about modified being allowed to dry overnight whereas if I put the tile down it wouldn't dry properly.
I would fill in the dimples first with modified thinset on top of Ditra making sure to fill in all the dimples, let dry overnight and then use the floor leveller the next day-- let that dry ---then install tiles.
I was thinking maybe using a sand topping mix (avoid runniness of the leveller under the drywall) but I think the leveller would do the job better to feather out the smaller spots. Plus I don't think sand topping mix had any latex additives unless you can mix some in?
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Old 03-15-2014, 10:13 PM   #4
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Leveller over DITRA


You can mix the latex into sand mix too, but I wouldn't add sand to a leveler. It's designed to level out of the box when mixed according to directions.

However I'd call Schluter and ask them if you can just pour the leveler over the Ditra, and avoid the 2 separate steps.
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Old 03-15-2014, 10:15 PM   #5
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Leveller over DITRA


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...However I'd call Schluter and ask them if you can just pour the leveler over the Ditra, and avoid the 2 separate steps.
Thanks- I think ill do that -- I agree no sand mixed in w leveller
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Old 03-16-2014, 12:00 PM   #6
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Leveller over DITRA


Sand mix would be completely wrong. Sand mix is to build a base and needs to be at least 3/4" thick.

Too late for you, but Ditra instructions specifically tells you to make the floor flat before you install Ditra, not after. Will it work now? I would say what choice do you have? It'll be extra work and you may lose the proper uncoupling effect.

To save self leveling or patching cement, filling Ditra is smart, but Schluter will tell you to use unmodified thin set.

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Old 03-16-2014, 12:53 PM   #7
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Leveller over DITRA


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It'll be extra work and you may lose the proper uncoupling effect.
I thought about it, and I can't imagine why you would. Assuming you mean putting the leveler on top of the current Ditra.

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