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Rapid Set Thinset Over Ditra?

12 years ago

Schluter recommends unmodified over Ditra but I've read in various forums that a fast setting thinset, like Laticrete 253RS is fine. Do you pros here agree? I can't find any info on how fast setting thinsets work - exactly how they cure; do they need air?

I should mention, tiles are 18"x18". I read a mongo post that recommends sticking with unmodified for large tiles but he didn't mention fast set stuff.

Thanks,

Bill

Comments (9)

bill_vincent
12 years ago
I have no problem at all using 253R over Ditra, especially if you prefill it, and then use the 253R to set the tile, as well.
bill_g_web
Original Author
12 years ago
Oh, so two steps: Fill the squares and then set the tile over the resulting flat/smooth surface. I've seen mention of this technique and if it's good for Bill V., it's good.

So I'm looking at:

Lay Ditra using the 253R.
Wait 2 hrs.
Fill ditra squares using 253R.
Wait 2-4 hours. (Will I need to be careful walking on the ditra with filled squares? I should probably lay some plywood over it to sit/kneel on while tiling.)
Tile over filled squares using 253R.
Wait 2-4 hours.
Grout/traffic.

Thanks,

Bill
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I totally relate to the nervous part. I take a long time to do things because of nerves. My DH says, "well of course it is taking time, you've never done this before". Very supportive. Here are the steps of my floor in pictures. I know this is beyond the scope of this post but here is a summary of my floor job. I have the tiled walls to do yet, and the sink (i'm making out of soapstone), and the cabinet man to install the cabinets. Getting the deflection corrected to accomodate stone tile. If interested in using a calculator for this go to the John Bridge forum. We added joist between existing joist. We screwed them to the subfloor on the top side every 6 inches or so. DH doing this awful job: 3/8" exterior grade filled AC (I think) plywood over 3/4" old subfloor and 3/4" fir tongue and grove. Screwed down 4"oc, though was supposed to be 6"oc, but I forgot those instructions :) so more work than needed: One of the many steps taken to waterproof my floor in prep for SLC, it is like water and will run out of your room into the basement or where ever: My heating wire installed. I calculated this layout almost to the last inch. That is because I drew out the layout several times to get it worked out on "paper" first (computer). I primed for SLC before I laid this out and again after the layout, being careful not to pool the primer (read that somewhere?) I also laid a plastic lath over everything and stapled it down every 4" or so, to provide strength to the SLC: Pour SLC, have help! Ditra down, before my patch repairs, I know you can do better than this :) Tiling: Finished floor. I used slate and Laticrete epoxy grout. Still need to caulk the threshold: If you haven't done so search for stacyneil's bathroom and the process she documents when she did her bathroom floor and the SLC job. Very helpful.
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bill_vincent
12 years ago
Ummmmm-- wait a second-- what're you putting the Ditra over? If it's plywood or OSB, you want to use 317 mixed with 333 liquid latex (or if you're getting it from Lowes, Megabond thinset mixed with the latex thinset additive) to get as good a bond as you possibly can to the wood surface. 253R's good, but it's not THAT good. (as far as I'm concerned)

As for after filling the squares, you want to make sure it's completely dry. Once it is, there's no need to use plywood or anything else. If you need something to kneel on, then you shouldn't be on top of it yet. One good thing about the 253R, though-- hands down, about THE fastest fast set I've used. Once you prefill the Ditra, it wouldn't hurt to put a fan on it.
bill_g_web
Original Author
12 years ago
OK, Re the ply to ditra bond. I've got some Versabond around - I'll use that. Or, I can get the Megabond and the latex additive. I've read that folks do use Verasabond for the ply-to-Ditra bond.

Thanks for the clarification. I was equating rapid-set with modified; not so it seems.

Thanks.
Bill
bill_vincent
12 years ago
Versabond has even less latex in it than the 253. yes, it says on the bag, just as it does on every single bag of modified thinset, that you can use it to bond to plywood. Don't believe it. Use the Megabond and additive.
bill_g_web
Original Author
12 years ago
Will do. Thanks much for the advice.

Bill
weedyacres
12 years ago
And here I thought that the thinset on top of the Ditra needed to be a monolithic pour. When I've tiled a partial floor and returned the next day, I've always chiseled out the dried-up stuff in the waffle holes before going over it with fresh stuff for the new tile.

I learn something new every day.
bill_g_web
Original Author
12 years ago
Hey Weedy;

If you google "Filling Ditra Waffles" you'll get a link to another forum, which I won't mention because g-web has rejected a previous post I attempted saying that site is a spam issue. (I doubt it - I think it's a competition issue.) I too was concerned about a cold-joint effect but that's doesn't seem to be a concern. The practice is discussed in the context of a modified thinset too. And the posts are recent; thread begins in 2009 and ends in June 2011.
bill_g_web
Original Author
12 years ago
OK, done with the floor tiling and what I've read on forums about using rapid set thin set, that it may not be something an amateur should use, is right. Wow. After pre-filling about 8 sq ft I aborted, got some Megabond and tiled; took all day to do a 5 x 7 floor.

Hat's off to pro tilers - hardest DIY job I've ever done.

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