Bathroom tile over new concrete [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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05-27-2003, 09:21 AM
It's almost tile time for our laundry room and 2.5 baths. Floor is concrete slab, new construction with stress cracks. Slab has cured for 14 months. No moisture problem that we're aware of.

I have seen homes a year old with cracks in the tile (slab foundation). One person I know bought a new home with sheet vinyl in the baths but he wanted ceramic. The builder laid the ceramic tiles on top of the vinyl. No cracks at all in the baths after 3 years, but plenty of hairline cracks in the kitchen where the ceramic was original with nothing under it.

I've heard it both ways--use an underlayment like sheet vinyl or tar paper (felt) prior to laying the tile, and don't use an underlayment because it will degrade and turn to a fungus.

Which is correct? We want to do this right the first and only time! I don't want cracks in the tile resulting from cracks in the slab.

Thanks in advance for any help! Dee

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05-27-2003, 09:53 AM
Hi, Dee! Welcome!

You do need a membrane over your slab. Vinyl flooring or tar paper are not acceptable. Check into decoupling membranes or anti-fracture membranes from either the Schluter company ( or the Noble company ( You may get away with applying the membrane over the cracks only, but I would do the entire floor, just to be safe.

John Bridge
05-27-2003, 04:16 PM
Hi Dee, :)

Yep, I've seen it all, too. I've seen floors laid over tar paper that have lasted forever. At least the tar paper is somewhat stable.

The problem with vinyl linoleum is that it is not stable. the top "wear layer" shrinks and become brittle as it ages.

We recommend using membranes that have been designed and tested for ceramic and stone tile installations. I would follow Bob's advice and do the entire floor area. The rooms are small. I personally recommend Schluter Ditra.

05-27-2003, 04:20 PM

After new concrete is poured, how long must it cure before
Ditra can be installed over it?

-Peter D

05-27-2003, 04:51 PM
ditra can be installed on " green " concrete , or concrete thas been cured less than 28 days

John Bridge
05-27-2003, 05:35 PM
Brian has it right , Peter. Let it firm up to the point where you can't trace your initials in it, and you're ready to go. :D

Seriously, the longer you wait, the better. I'd give it a couple weeks or so.

05-27-2003, 07:40 PM

Once Dita is put over the green concrete, how does the moisture escape?


05-27-2003, 08:20 PM
I think they address that on the Schluter site. It works because it's groovy baby, Yeah! :)

Art in Stone
05-28-2003, 11:47 AM
I believe that Ditra is the ONLY way to go when tiling on a green slab. I wouldn't do it any other way.