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Tile prep - concrete floor with radiant heat

15 years ago

We're about to lay 1200 sq ft of tile on a basement (walkout) concrete floor with radiant heat (new construction).

There are a couple of expansion joints and some cracks near the edge.

What needs to go under the tile (most likely ceramic 13 x 13)?

Is Ditra necessary? Or are there less expensive approaches?

Thanks

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Comments (7)

bill_vincent
15 years ago
If you have cracking, then yes, I'd say Ditra is necessary. Also, Even with the Ditra, you still need to honor all expansion joints in the concrete. Additionally, you want to make sure you have soft joints in the tile atleast every 15 feet.
sharrongrant58
Original Author
15 years ago
Bill, Thanks for the response...can you clarify what you mean by "honoring" the expansion joints, and "soft joints"?
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bill_vincent
15 years ago
By honoring the expansion joints, I mean that those joints ned to have the Ditra cut through, and the tile either laid out to fall with a grout joint there, or cut the tile to those joints and caulk them. Those joints are in the concrete to allow for movement, and the tile's not going to stop that movement. So you need to have a joint all the way through, and then caulk that joint.

What I mean by soft joints is that the joints in the concrete may not be every 15 feet, and you need to have a caulk joint in the tile every 15 feet to allow for expansion and contraction of the floor. So if the expansion joints in the concrete are, say, 18 feet apart, you'd want to put a caulk joint in the tile at about 9 feet.

Now before you get upset that you're going to see these glommy joints throughout the floor, every grout manufacturer makes caulking in the very same colors as their grouts. They even come in a sanded an unsamded version to match the grout more closely. You don't even hardly notice them. Matter of fact, I just saw a customer whose 800 foot floor I did about a year ago, and that was her main concern-- that she'd see those joints sticking out like a sore thumb. She said she never even sees them until she washes her floor, and then of course the grout joints darken up until they dry, while the caulk joints stay the same. Otherwise, she said, she'd never even see them.
sharrongrant58
Original Author
15 years ago
Bill,
I was wrong - there are not expansion joints - they are saw cuts - don't go all the way through. Does that change the approach?
Thanks
bill_vincent
15 years ago
Yes, it does. You still need the joints every 15 feet, but you don't need to honor those joints in the concrete, being that you're going over the whole thing with Ditra.
sharrongrant58
Original Author
15 years ago
Bill,
Thanks again - still feel the ditra is needed though?
My contractor claims they've had sucessful installs in similar situations without it.
I am looking to save the money if possible, and I'm willing to live with some cracked grout.
bill_vincent
15 years ago
still feel the ditra is needed though?

Absolutely. But your contractor's the one warrantying the floor, so if he says he can do it without the Ditra, so be it..... so long as you trust his warranty.

And just for the record, you SHOULDN'T be willing to live with cracked grout. Why "settle" when spending this kind of money?

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