modified or unmodified thinset over redgard

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Old 04-19-09, 11:52 AM
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modified or unmodified thinset over redgard

I am tiling a covered/enclosed porch area with porcelain tile. I've put down RedGard as an anti fracture membrane over the concrete slab. Should I use unmodified thinset to set the tiles for the very same reasons that one uses unmodified over Ditra? Or doesn't it matter?
JoeP
 
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Old 04-19-09, 06:56 PM
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Joe,

Redguard isn't Ditra, they want you to use a good quality modified thinset over it.

As you know, unmodified is recommended over Ditra, even when installing porcelain. But Redguard doesn't offer anywhere the uncoupling as does Ditra. So you gotta use modified over Redguard, or you will have a failure within a short time.

Jaz
 
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Old 04-20-09, 05:19 AM
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Thanks for the reply. It appears you were right on! I did find a reference to using modified thinset at the RedGard web site in their FAQ section.
Again, thanks.
 
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Old 12-27-11, 08:43 PM
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OP raises a good point, the same one I see asked elsewhere with no clear answer.

Yes, I know this thread is two years old.

Schluter says to use unmodified mortar, which does not need to dry (rather it cures when moist, like concrete) between the ditra and the tile. Modified thinset on the other hand has to dry, so between moisture-impervious ditra and the tile the only way to dry is between the joints (modified between the ditra and substrate, since chances are the thinset can dry into it).

So, why does Custom Building not recommend unmodified between the redgard and the tile? Not sure But, the redgard instructions I have read in detail now say nothing about having to use unmodified. Moreover, the Flexbond modified thinset (sold at HD, for example) specifically lists redgard as one of the surfaces it can be applied to and therefore, following manufacturer recommendations, a person should be using a modified thinset like flexbond over Redgard.

That said it seems to me it would prolong drying. If you laid a 12" tile over redgard and assume the redgard is essentially not moving any moisture and neither is the tile, the center middle of that tile's moisture has to now dry through 6" to get to the side of the tile.

This is all academic I am certain, just something to worry about when in reality you can almost surely put the tile on the redgard, wait the 24 hours before walking, grout it and be done
 
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