# moisture vapor problem in slab on grade



## dutchko (Feb 14, 2010)

Removed laminate to install tile and found nasty mold between concrete slab and "moisture barrier" and also between that barrier and the laminate.

Mold test before removal were negative.

Clearly a moisture vapor issue thru the slab (on grade)
Plastic sheet test was positive and I am waiting results on "calcium chloride test" (72 hours)

The slab has no moisture barrier installed under the slab.

Read that products like "red guard" or "schluter-ditra" are not really for moisture vapor from the slab.:sad:

Has anyone ever used "Radonseal" (deep penetrating concrete sealer)??

So far all my research showed the only real fix being to install a moisture barrier UNDER the slab.
Minor problem is that I have to remove the whole HOUSE first.

So, the question is; Is there a reliable penetrating sealer that won't let loose in a couple of years.

And if I install porcelain with 1/8" grout lines, will it transmit the moisture and create poor air quality in the house:shutup:

Another issue that comes to mind: if I can successfully seal the concrete, will the moisture come up thru the interior walls instead?? (can't seal under that)


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## angus242 (Oct 20, 2007)

dutchko said:


> "schluter-ditra" are not really for moisture vapor from the slab.


:blink:


Directly from Schluter:
_"c) Vapor management
The distinguishing feature of Schluter-DITRA is the existence of free space created by the configured channels on the underside of the matting. The free space provides a route for excess moisture and vapor to escape from the substrate that could otherwise cause damage to the tile layer above. Thus, DITRA effectively manages moisture beneath the tile covering."

_You need to be better informed, my friend.


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## jarvis design (May 6, 2008)

Listen to Angus!!


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## dutchko (Feb 14, 2010)

_"The free space provides a route for excess moisture and vapor to escape from the substrate_"

And route where??, under the wall, like sweeping dust under the carpet?:whistling
'cause at the wall the schluter paper will end, so that would mean it channels the moisture vapor into the wall and "hello mold":blink:

any word on that deep penetrating sealer from "radonsealer"?

Thanks for the input:thumbsup:


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## angus242 (Oct 20, 2007)

dutchko said:


> any word on that deep penetrating sealer from "radonsealer"?


You cannot lay tile over sealed concrete.

If you have a hard time believing me about Ditra, do the research on your own.

My advice, make sure the slab is clean of all foreign materials, Kerabond, Ditra, Kerabond & tile.

Done :thumbup:


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