Replies

1. 
   DickRussell | Jun 24, 2009 08:47pm | #1

   Since the PM is porous and below that also is porous, I suspect Schluter doesn't want unmodified down there. I would think the PM would be suitable for bonding the Ditra to the PM already down and cured. The unmodified is what Schluter wants between the Ditra and tile above it.

   [Edit:] On looking closer at Schluter's documentation, I see that for bonding Ditra to a concrete substrate they recommend unmodified thinset, although they suggest making the concrete surface damp before applying the thinset. I wonder if the surface nature of concrete and cured PM are similar and would call for unmodified thinset for laying down the Ditra.

   That leads me to a related question. For my first tile job, I put Ditra down over plywood using Hydroment Single Flex, which like the PM also is "modified." OK so far. I had asked for an unmodified thinset for laying tile over the Ditra, and they gave me a bag of PM. Last night I laid down part of the tile over the Ditra using the PM. On looking up what the PM is, and that it meets ANSI 118.4 and not 118.1 (recommended by Schluter), I am wondering if I should continue with the PM for the rest of the floor or go back for the "Tile Mate," which meets 118.1. Since part of the relatively small floor (about 5x6) is tiled already, is everything going to come out OK if I finish with the PM? If I need to give it more time, how much time to be safe? Anyone put tile over Ditra using PM?

   
   

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   Edited 6/24/2009 2:02 pm ET by DickRussell

1. 
   SRSprague | Jun 24, 2009 10:06pm | #2

   The surface nature of concrete and the cured PM in my new bathroom appear to be similar: a smooth membrane over-all; until after I ground down some high spots on the PM, exposing the interior nature of the PM: HIGHLY porous, even sponge-like but rigid. I could not keep the cured PM wet enough to even spread the CustomFloat Bedding Mortar I tried to use under the DITRA yesterday; talk about frustrating. Today, I found that none of the DITRA I had put in place stuck; more frustration.O.K. So, I put PM on PM under DITRA. If I follow the mixing instructions on the PM bag, I get Play-Doh. Last time I used PM, I just added water until I could spread it. However, it was like spreading tar; it stuck to everything big enough to get it on, including my trowel. How do I manage such stuff?