repairing slope of shower floor
I bought a totally-rehabbed home a few months ago with a huge walk-in shower. There is a single drain, at the south end, but the floor peaks in the middle, so half the floor slopes to the drain in the south end, but the floor to the north of the middle slopes to the end where there's no drain, and water thus pools. The builder/seller is going to fix it. His current suggestion is, since the current floor is functioning correctly in terms of water tightness (the assumption is that there's a properly-installed shower pan under the tile and no leakage), to install a new properly-sloped floor on top of the existing tile floor. The existing floor is a pretty mixture of 2 x 2 and some larger tiles, but I don't care if we go with all larger tiles for the new floor. I just want to know, first, if there is any problem with installing a new tile shower floor on top of an existing one. Here's exactly what the builder/seller proposed: "We would use a brush on water proofing membrane just for added sealant. We would slope the tile the appropriate way and bring up the floor drain as needed. We could lay the tile in a variety of designs. The logic is to not disturb an already functioning tile pan." Thoughts???