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Thank you dan1888, I will show my installer.

At the risk of sounding like a dick, if your installer doesn’t know what a decoupling/crack isolation membrane is, I would absolutely, 100% find a new installer.

IMO if your installer is not familiar with this basic material get a new installer who has kept up. BTW where are you putting the tile ? If just on the floor make life simple and do vinyl tile no issue with a bit of movement if shower walls then a rip out and new waterproofing has to be done.

I cannot deal with the dents that ultimately occur in vinyl, even the newer vinyl, I'm just a porcelain, ceramic or stone person. I am just tiling the floor and not walls at this point. Thank you for your note.

I think if you go with the ditra it should work. FYI I have done vinyl tile installs in 5 bathrooms for clients and not one has had an issue with dents , not really sure what would dent a floor in the bathroom that would not break a tile.

arch13, I was talking to my installer by email and just called it a "membrane" to limit cracking. He knew about waterproofing membranes. I had no clue if they were the same thing. It was probably my fault and just my communication -- I didn't know the correct term, I never called it decoupling/crack isolation until dan1888 provided info with the correct terminology. I'm sure he knows what it is.