Need Help. Should i Use Ditra Mat or something else? Thanks!

[chris87]

Hello,
I want to tile my concrete floor and I am unsure of what type of underlayment to use due to some concerns I mention below:

Details:
-In NY (lots of heat & freezing)
-Raised Ranch, Built in 2005. (tile to be installed on concrete slab on ground floor)
-Cracking around perimeter of concrete floor. Some parts near the walls are slightly elevated where cracked.
-MARAZZI 24 in. x 6 in. Glazed Porcelain tile

Additional info:
Previous home owner installed laminate flooring on the slab with a plastic vapor barrier in between. Once removed, I found mold on the concrete. There is also a nail hammered into the concrete that is rusted, which tells me that there is moisture coming from the slab. I’m not sure if it’s an abnormal amount or a regular amount of moisture coming thru.

I had the following questions:

1. I was thinking of cleaning the slab and evening out the cracking as much as possible with a thinset or sealer of some sort then to use Ditra mat over the floor but I am paranoid of it trapping moisture. Is this the correct route to take?

2. What type of thinset should I use above the Ditra and below it, if Ditra is the way to go?

3. How large should my trowel lines be for the Ditra mat and for the 2’ x 6” tile?

Any help would be greatly appreciated.

Thank you

 

[FloorMaven]

Ditra is an uncoupling membrane designed to accommodate subfloors that have some movement. Usually these are wood subfloors or active concrete slabs. Your crack around the perimeter is probably between the slab and stem wall. This is really not a crack but a product of the design, as slabs and foundation stem walls are poured at separate times.

I would do moisture tests and mitigate as necessary. Then install on slab using a thinset application.

 

[happyhours]

yep, sounds like an old slab which shouldn't need the Ditra being it isn't cracked and probably won't.

 

[happyhours]

Modified Thinset to set Ditra

Un-Modified to set tile

[ had to look it up ]

 

[DarisMulkin]

There is Ditra Set that can be used to set the ditra and the tile to the ditra.

Daris

 

[rplace]

Wouldn't use Ditra, moisture test the concrete if all is well use a crack isolation membrane and set your tile, I would go with a 1/4 1/4 1/4 trowel

 

[rugaddict]

imho ditra would be overkill---they use it on cement to deal with expansion joints---if you dont have movement---you dont need ditra

 

[DarisMulkin]

It is also used if there are cracks. If it cracked once it will crack again-just saying.

Daris

 

[rugaddict]

spot on my good man----cracks do mean movement---if there are no cracks----a cement slab is as good of a subfloor for ceramics as you could hope for