Kerdi = Unmodified, Ditra = Modified - Why?

 
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Old 07-13-2010, 09:17 PM   #1
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Kerdi = Unmodified, Ditra = Modified - Why?


Gentlemen,

It's been a while. Hope everyone is well.

Anyway - here's a question that has stuck in the back ofmy mind for some time:

Install instructions specify un-modified thinset between Kerdi and the tiles. Schluter's official explanation is that the impermeable Kerdi will not allow moisture to escape, causing polymer-modified mortars to not cure properly.

But Ditra instructions specify modified thinset between the Ditra and the tiles - and Ditra is no less impermeable than Kerdi.

Anyone know what's really going on?

Thanks.
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Old 07-13-2010, 09:26 PM   #2
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Re: Kerdi = Unmodified, Ditra = Modified - Why?


Bob, modified for ditra when installing over wood sub-floor, un-modified is what schluter wants between tiles and ditra. I like kerabond.

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Old 07-13-2010, 09:29 PM   #3
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Re: Kerdi = Unmodified, Ditra = Modified - Why?


Quote:
Originally Posted by bob_cntrctr View Post
Gentlemen,

It's been a while. Hope everyone is well.

Anyway - here's a question that has stuck in the back ofmy mind for some time:

Install instructions specify un-modified thinset between Kerdi and the tiles. Schluter's official explanation is that the impermeable Kerdi will not allow moisture to escape, causing polymer-modified mortars to not cure properly.

But Ditra instructions specify modified thinset between the Ditra and the tiles - and Ditra is no less impermeable than Kerdi.

Anyone know what's really going on?

Thanks.
You've got it wrong. The ONLY time modified thinset is used is UNDER Ditra when installed over WOOD.

Always unmodified OVER Ditra. Unmodified UNDER Ditra over concrete.
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Old 07-14-2010, 07:12 AM   #4
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Re: Kerdi = Unmodified, Ditra = Modified - Why?


You know, I just installed about a mile of Ditra a couple months ago, and I know I did exactly that - modified underneath 'cause it was going over 3/4" plywood, then unmodified on top. But the brain must be getting old, I remembered it backwards, and realized it made no sense that way....

Thanks for jogging the old memory.
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