Schluter Ditra Mat on concrete slab

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Old 01-04-12, 11:35 AM
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Schluter Ditra Mat on concrete slab

We are in the process of building a cottage and I wondered if we needed the extra expense of the Schluter Ditra Mat under our planned slate tile flooring. The floor is a 4" poured concrete slab on grade with moisture barrier and 2" SM insulation under the concrete. We also have an in-floor glycol heating system.

The Ditra will cost approx. $3,000 and I am not sure if we really need it on a concrete slab. Are we taking a big risk by installing the slate tile without Ditra?

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Old 01-04-12, 12:04 PM
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No, at least not in my opinion. Sounds like you already have a well prepared surface. Tiles will be secure and solid without movement.
 
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Old 01-04-12, 12:17 PM
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Nope, I think you're fine without it as well.

Just one note, don't do anything with the concrete surface like sealing or painting it before you put down the tile.
 
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Old 01-04-12, 05:33 PM
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I highly disagree with the suggestion of just tiling over bare concrete. Especially new concrete in a large area. I would use some kind of membrane, Ditra being my first choice.

The $3k is irrelevant since it must be a large area. If the Ditra will cost 3k installed, the rest of the tile work must be worth 15-20k, so I wouldn't take a chance on having a failure to save 3k.

Jaz
 
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Old 01-04-12, 08:29 PM
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While I understand at least some practical applications using products such as Ditra in regards to waterproofing and eliminating floor tile flex failures, I would like to further understand the necessity for applying it over an insulated, and heated concrete floor. What kinds of failures based on years of not having this kind of product are now being addressed if used over such a prepared concrete pad? As I would have considered such an application 'overkill', that is only based on my very limited knowledge and personal experience and considering the amount of applications that have not ever failed both in commerical and residential installations prior to Schluter type products. That said there must be many others on this forum who would have thought as I have and would also benefit from more insight into this requirement.
 
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Old 01-06-12, 07:48 AM
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Thanks for your replies. We are having a hard time making a decision because the "experts" (suppliers and installer) are of course trying to sell us more products and an honest opinion is not always easy to come by when money is involved.

In reply to JazMan, yes the area is large 30 x 40 and the job is a substantial amount of money already without the added Ditra Mat.
 
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Old 01-06-12, 08:05 AM
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Jaz knows more about this stuff than I do, his opinion of the mat being a good idea would make me rethink my position.
 
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Old 01-06-12, 09:26 AM
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I completely agree with Mitch17 in regards to my knowledge levels also, and that is the reason I hope that Jaz would help explain more of the 'why' as the 'what' and 'how' are known. I am probably just trying to understand as is the OP the cost/ risk benefit rationale for any tile over concrete scenario. The only one I can think of is potential settling cracks of the pad on grade itself and I would guess that the degree of exposure involves the kind of pad structure used and ground soil /climate and moisture conditions. I have seen cottage pads built on several feet of natural sand and gravel locations near lakes in cold climates that always drain and don't even really have winter ground frost issues.
 
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Old 01-06-12, 12:34 PM
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What the flooring company is doing is basically selling a insurance policy on the installation, and to a extent for the homeowner. Without knowing as stated, the installation method of the slab...expansion joints, zoned heating, was the slab "floating", poured to the footer or on top of it, etc. Shlutter Ditra says that their product is ideal for heated floors because of the expansion rates of tile and concrete. A area this large needs expansion joints or something to reduce the chance of a failure. without it you run a higher risk of "tenting" or spalding of the slate from pressures.
 
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Old 01-06-12, 07:17 PM
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A concrete slab will shrink as it cures which is why you see hairline cracks or even a bit wider than hairline. This process can take well over a year. If no method is used to help isolate the tile work from the slab, bad thing can happen.

Aside from expansion joints in the field and at certain doorways or "L" areas, you of course have to maintain expansion joints at the perimeter. This is "normal" installation technique regardless of wether a membrane is used or not.

I highly recommend a sheet membrane, Ditra is my favorite. Noble deserves consideration too. (might cost more though). Another way is to go with a liquid membrane such as Redgard or Hydroban. A third way it to use a crack isolation mortar. Some mortars claim isolation protection up to 1/8". Better than nothing.

Jaz
 
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Old 01-06-12, 08:54 PM
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From my perspective a big thank you to the experts below. I have learned something I didn't know, and like many on these forums, (for me often the automotive ones) I read and write to help in areas I can also based on my training and or experience, and always read to learn more in specific areas I don't know enough about.
 
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