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Unread 02-06-2003, 05:20 PM   #1
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How waterproof is thinset?

I just watched a Schluter-Kerdi Drain video over at thier website. The stuff looks great and I'm too far into my install to use it, but it raised some questions.

In the install they used modified thinset for all of the Ditra seams with a 2" overlap as well as the the drain itself. This, they say, gives a waterproof install.

Is modified thinset that waterproof? I knew it was more resistant than plain thinset, but not waterproof. Won't it still draw moisture up into the joints?

If it is that water resistant, should I use regular thinset to set my floor tile to help with evaporation?

Oh, before I forget, I was reading on another website that "good" contractors use a ribbed mat between the liner and the mud to aid water runoff. I've not seen such a product, but I had been thinking about that same thing. Is there such a thing? Do "good" contractors use it.

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Unread 02-06-2003, 05:46 PM   #2
Tile Setter
Join Date: May 2001
Location: Austin, TX
Posts: 4,840
All portland based cementious products will allow water to pass through. The latex modified is more resistant due to the latex that is mixed in with the adhesive but that doesn;t make it "waterproof".

The latex also allows a bit more flex in the tile and substrate.

You can use either thinset you wish but I highly recommend the Versabond. Laticrete and Mapei also make good modified thinsets

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Unread 02-06-2003, 05:54 PM   #3
Rob Z
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Hi Adam

As Jason described, thinset itself isn't waterproof. It isn't degraded by water, and does resist the flow of water (somewhat), but definately does not "waterproof" any tile installation the way a membrane will.

Kerdi works at the seams because the very small openings in the thinset between the layers of Kerdi resist the flow of water. The openings are so small that the surface tension of the water molecules/droplets is greater than the pull of gravity or head pressure in the column of water above. Simply said, the water molecules are more attracted to the Kerdi and thinset than they are inclined to flow through.

Kerdi does work very well. When we were at the Schluter school at the TCA/CTEF, we saw ordinary cardboard boxes that were lined with Kerdi, and had been holding water for months.

The rbbed material you read about may be Schluter Troba. I use it on top of the pan liner and under the mud bed in a shower floor. It does facilitate drainage along the pan liner to the weep holes in the drain.
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