What about a couple of coats if AD on top of the mud bed?I guess it never really changed. I would never do a standard mud bed so I guess it just never got brought up. If you look at the instructions on installing urethane over a mud bed, it says to wait so ridiculously long period of time...or maybe not to do it at all. The slow cure with all the moisture attacking the urethane from underneath can cause softening of the grout or that white powdery stuff that looks like efflorescences.
I guess I was thinking of a liner and mud bed, at that point the AD would be a barrier between the tile and moisture coming from the mud bed. Just a thought. Not a whole lot of thought.That's fine...well, maybe not. I only use a fabric membrane because it helps me sleep at night. Regardless, you can't just drop some liquid on a standard mud bed and call it a day. You need to use the "divot" method or Noble Drain Flashing method to do so.