On the third try, I've finally received an undamaged Sterling Ensemble four piece tub-shower unit. Today I ripped out the old tub and tomorrow I hope to begin installation of the new one, but a couple of surprises have come up...

The old tub was set in place on 1/2" plywood, and then the previous homeowner decided to tile the floor next to the tub, so he added a second layer of 1/2" plywood + tile. The difference between the plywood surface where the old tub sat and the tile floor surface is 7/8". The new tub is about two inches wider than the old one, so the new tub's skirt will sit on top of the tile, whereas the tile butted up to the side of the old tub's skirt. Ergo, I believe that I need to build up the floor under the new tub by about 7/8". That's fine by me, because I was not impressed to discover just 1/2" plywood under the old tub.

But the floor is seriously out of level: the drain end is 1/2" or maybe even 5/8" higher than the other end. The skirt will be above the tile, so to install the tub level, I'm likely to be looking at a 1/2" or 5/8" gap between the tile and the skirt at the back end of the tub. That is at least a cosmetic problem, and I'm also wondering if it might be a structural problem? (Sterling doesn't indicate if the skirt needs to be in structural contact with the floor or not).

Does anyone have ideas on how to address the cosmetic issue? I don't think tub caulk is going to work very well for a 5/8" gap.

If it was some material other than tile, I might try to trim back the flooring material so that it butted up to the skirt, rather than having the skirt on top, and that would hide the large crack. But I can't think of any reasonable way to trim tile that is already grouted down. That's not feasible, is it?

On a related note, I'm planning to install 3/4" plywood under the new tub and on top of the existing 1/2" plywood, to make up most of the gap, and then shim the four corner feet to get it perfectly level, and then use a mortar bed to support all the other feet. But it occurred to me that I could rip furring strips to the thickness I need, place them over the existing 1/2" plywood and on top of the joists, and then lay the 3/4" plywood on top of that. The 3/4 plywood would then be level and it would be supported 16" oc by the furring strips, but it would not be lying flat atop the existing 1/2" plywood. It sounds like a reasonable approach, but I've never heard of anyone doing this, so I'm shying away from the idea. What does anyone think about putting the shims under the new plywood layer, rather than on top?

Any thoughts appreciated.