Major screwup, used modified mortar between tile and Ditra, salvagable?

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MarkZ2

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Hello, apologies for just making my appearance by starting a thread.

I have a bathroom in a recently purchased rental that I completely gutted due to mold and water issues.
Most of the renovation went ok. but when it came to the floor, there was a communication breakdown and polymer modified mortar was used.

floor joists are 16", covered by 3/4" shiplap, then the shiplap was covered in wood glue and 1/2 plywood was screwed on top with 1" drywall screws 4" apart and the rows staggered.
Then polymer modified mortar was used to adhere the Ditra to the plywood AAAANNND it was continued to be used for the tilesetting. the tiles are 12"x 24" and the spacing for the grout is very thin, like 1/16" or 1/8".
The ditra and the tiling was done in one day, today... and I don't find out about this till a couple of hours ago..

Now, by reading these boards the last few hours, I have learned that if the polymer modified mortar is given a loooong time to dry, like 3 weeks or possibly 2 months but not likely less than 2 weeks it will eventually dry and cure and should be fine. However, I have had to put my tenants up in a hotel to do this so that is impossibly expensive. Other comments I have read are to the effect that in 3 days the tile mortar will still be soft enough to pull the tiles off.

I have a tile guy coming tomorrow to finish with the wall tile...

So my thoughts are to get plywood down over the tile tomorrow morning so the wall tiler can do his work and stand on the tiles put in today over the plywood (I know it's bad to walk on but I will probably be pulling them anyways and by some stoke of luck the tile might be protected enough by the plywood. Then when the wall tiler calls it a day, put space heaters in and a fan to try to get the room to 30 degrees C ( relative humidity is 38% quite dry) and leave it that way for Sunday night, then come Monday, try to pull a tile off to see how easy/hard it is to do, if its easy then pull them all, take them outside and power spray the modified thinset off. Then clean off as much of the modified thinset off of the ditra and redo it with unmodified like it should have been done in the first place. I don't want to pull the tile tomorrow or Sunday because I am hoping that the bond between the fabric backing of the ditra and the wood will be adequate by Monday. I am trying to avoid having the entire system get pulled up with the tile, or any air bubbles forming between the ditra and the wood which will allow flexing and the breakage of future tile. If by some miracle the tiles are stuck on really well by Monday (I have read that some polymer modified thinsets have a lot less polymer, might get lucky), I will leave the plywood on and let the tenants move back in. then in 2-3 weeks I will get it grouted.

As if things couldn't get much worse, I had to go out of town for work and won't even be able to be there to help...

How barking mad am I?
 

Jadnashua

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There is more than one type of modifier...some do not need to air dry to attain their stated strength. If it is a latex modified mortar, it does need to dry, though. So, what brand and specific type of mortar did you use?

Second thing, though, you should never glue plywood to a dimensional wood subfloor that you intend to tile! Several reasons, but one is that you want a bit of decoupling, and the glue doesn't help, plus, unless you used a full spread liquid wood glue like Titebond II or similar, and if you applied a construction adhesive with a caulking gun, you've added more gaps, even with the screws.

A bathroom may see a lot of traffic, but it tends to be one person at a time. With a small grout line, and those large format tiles, you are likely to need a long time for things to dry out. A porcelain tile (you didn't say what type of tile, but it's likely porcelain) has an absorption rate of much less than 1% by weight, so nearly no moisture will evacuate via the tile, which leaves only the grout lines.

Pulling the tile may also tear the fleece off of the membrane. This is a tough call. I'd wait to grout as long as you can, and then, not use a one-part or epoxy one, but a 'normal' cement based one which can breath a bit. It will slow things down.

You might be fine, depending on the thinset used...
 
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