I will be tiling a bathroom with a floor that slopes approximately 1.5″ over 11 feet. Because of this slope, the bottom edge of the level bathtub at one end is raised about 3/8″ above the subfloor (see image). I am wondering how to deal with this gap between the tub and subfloor — it is higher than the thickness of the tile, so I am concerned that it will both look bad and be difficult to make waterproof.
A couple of notes:
1. It isn’t feasible to level the subfloor because doing so would create an unsightly and unsafe tripping hazard at the threshold to the adjacent bedroom floor.
2. The subfloor is 3/4″ Advantech and I will be using Ditra underlayment.
My initial thought is to apply a layer of 1/4″ plywood over the Advantech to reduce the gap enough for the tile to look right against the tub. That solves the aesthetic problem. But how can I seal the gap to keep it waterproof?
I look forward to any suggestions you may have.