If you're looking to waterproof the floor, run the Ditra up to the shower pan, and cut it nice and uniform, leaving about an 1/8" gap, and then caulk it. Also, pick up a roll of Kerdiband to seal up the seams in the Ditra.

If I correctly recall your saga, you had a supposedly well built mud bed with supposedly well installed marble tile over it. Then you brought in a friend to seal it. After sealing is when you had the issues. If I recall, when the drain was later pulled, there was evidence that the sealer had percolated down into the mud bed. In a properly working shower, tiling over existing tile can be done. My understanding is your shower is broken. My understanding is that what forensic work has been done to your shower has not resulted in a cause of failure. It has only resulted in people pointing fingers at the other guy. The sealer guy points at the tiler. The tile guy points at the sealer guy. The GC shrugs his shoulder and points at you because you brought in the sealer guy on your own. You point at the GC and ask when will my shower be fixed? If no one can define the problem, how can they come up with a solution? They can't, so they all wink at each other and say "let's cover it up!" The only way to properly install new tile over bad tile that is on a bad mud bed is to completely isolate the new work from the old. There are three important points of contact: That means a NEW membrane has to be installed on top of your old work to prevent water from percolating down into the old work. That means that around the floor perimeter, the new membrane has to be tied into the wall's drainage plane or the wall's membrane that was installed behind the current wall tile. That means that the new drain has to be properly detailed into the old. So, what can you do? You can simply do what has been recommended. Simply cover over what you have. Bury it. Fingers crossed. Hope for the best. It's the easiest. You might have no further bad symptoms. Or the pan might start showing problems, 6, 12, or 24 months down the road. Or you can cover it up keeping the three points of contact in mind. Do understand that this route would require a conscientious and competent mechanic. Or go with the choice that over the long run will likely involve the least amount of labor, be the least expensive solution, and have the greatest chance of success: Have a competent mechanic remove the failed bed and install new. I wrote too much. (sigh) Good luck!

We are doing master bath remodel and previous owners had vinyl plank flooring laid over the concrete foundation-- the people who did the work said that if the baseboard is high enough (ours is about 3" of wood--not tile.. they said the vinyl plank was run to the baseboards and cut to fit then silicone caulk was used along that joint... So far have noticed no issues anyplace in house this was done--not just in bathroom... we are taking out all LVT in master suite and replacing it with 1 type of flooring for unified look after master bath is redone--since we can't get the type of flooring in there now--not made anymore-- they won't need to add a quarter round on top of the LVT... so as long as you are happy with how the LVT would look butting up to the ceramic tile baseboard--maybe you can do the same... IS the ceramic baseboard in good shape? Still tight?

Thanks for your answers! glennsfc, Sorry I don't know the technical word for that. But with the word "peeling" ceramic, I meant the top coat of the ceramic tile is peeling off in a few spots on the tiles. There're not a lot of those but I just know they're there... I read on this blog that a lady installed vinyl tile on top of the existing ceramic tiles. I wonder if anyone has that experience? The ceramic tiles I have right now is not in extremely bad condition, just a few "peeling" spots, very light color and stained yucky stained grout. http://www.sasinteriors.net/2012/10/installing-groutable-vinyl-tile-lowes/ So I wonder if there's anyway to work this out... with a baby in the house, I don't really want to make a big mess. Plus I don't have a lot of time to do that... :( .