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Unread 01-03-2020, 01:18 PM   #1
Scancoder
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Ditra issues with heated concrete floor?

We are about to have ceramic tile installed in a small sunroom, over a new, insulated concrete slab with in-floor heating. One of our contractors insists that DITRA be used, in case of slab movement (hard to imagine), which would cause tile cracking. The other contractor insists that DITRA be avoided because it will inhibit the floor's ability to heat. So, we are caught between two experts, both of whom are very competent and trustworthy. Any thoughts on this dilemma?
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Unread 01-03-2020, 03:47 PM   #2
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Welcome to the forum.

I would agree with the first contractor. With concrete, it's not a matter of "if" the slab will crack, but "when".

HOWEVER, Ditra is not a crack isolation membrane, so to prevent any future cracks from damaging the tile, you need a membrane that has been tested and proven to prevent cracks from transferring to the tile surface.

One such product is Laticrete Stratamat. It installs and functions much like Ditra, but will absorb movement from cracks up to 1/8" wide.

I assure you that the amount of heat lost through the plastic membranes is negligible. And even if it did lose some, it would be better than having a future crack damage a number of tile, requiring replacement.
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Unread 01-03-2020, 07:40 PM   #3
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Nobleseal CIS is also a option. Meets high performance for crack isolation o f over 1/8” and great for heated floors with a R value less then 1..
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Unread 01-04-2020, 01:23 PM   #4
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Noble CIS is exactly the product that I would use in that situation. It's a thin sheet membrane (under 1/16th inch) and is a ANSI 118.12 Crack Isolation Membrane.

Don't forget to put movement joints in the tile.
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Unread 01-06-2020, 09:51 AM   #5
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Hi Mark,

When Ditra is used in a situation such as yours it goes beneath the heat directly to the slab, so there is no way it could inhibit heat. Schluter also has a product called Ditra-Heat. Check it out. https://www.schluter.com/schluter-us...r-Warming/c/FW
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Unread 01-06-2020, 10:37 AM   #6
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I think his heating is already embedded in the concrete, John. Ditra would need to go on top.
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Unread 01-06-2020, 10:51 AM   #7
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Many thanks!

I very much appreciate all of the helpful and thoughtful comments!
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Unread 01-06-2020, 05:17 PM   #8
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The heat will work, its response will be a little slower. But, with radiant heat, often, the best practice is to keep it on as the thermal mass just doesn't change much. Having it above, and closer to the tile is useful if you are using it for warming versus area heating. For example, in CA, floor warming, done by electrical heating elements, must be on a timer, and cannot be used for area heat. Hydronic, in the slab, does not have that restriction.
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Unread 01-16-2020, 12:21 PM   #9
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Thanks for the comments

I appreciate all the great input. Yes, the heating is in the slab, so the isolation layer is between it and the tile. Our tile seller is now researching the alternative products mentioned in this thread. The contractor who is against Ditra is remaining insistent that no isolation layer is needed because of his reinforcements and insulation; however, this argument is not persuasive to us. We are happy to pay for the insulation layer. We are giving this contractor the option of building the sunroom but letting the tile seller do the tile installation. The tile seller is willing to guarantee all his work.
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Unread 01-16-2020, 07:20 PM   #10
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Will your contractor guarantee your slab won't crack? I doubt it. I would use an anti-fracture membrane of some sort over the whole slab.
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Unread 01-17-2020, 12:39 PM   #11
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The main contractor believes the slab won't crack, and yet he won't guarnatee it. We agree that some form of anti-crack/isolation layer is needed. At this point, we have offered to let the main contractor off the hook for the tile part of the job, and just let the tile seller install the floor (used him before, and he is top notch, plus comes with full guarantees). The main contractor seems to believe that the tile seller is just trying to sell more stuff, which we are certain is not the case.
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Unread 01-17-2020, 08:05 PM   #12
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If you expect the tile contractor to stand behind his work, let him put down an anti-fracture membrane like he wants to.

When I bid a job over a slab, I automatically figure in a membrane to cover the whole floor. If you don't want one, then you don't want me to tile it. Simple as that.
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Unread 01-20-2020, 08:02 AM   #13
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Thanks Davy. That's pretty much how we see it: the barrier is essential for tile over concrete slab. It is very awkward for home owners when they get caught between professional contractors who have polar opposite and strongly held opinions. This forum has been very helpful to our understanding of the situation.
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