Lenore, who is installing the granite slab shower? Start there and make your priority be hiring a VERY experienced tile professional - one you have vetted carefully to insure that their qualifications meet your design requirements and product selections. Stone slab installations are not for the B team, and especially in a wet area. Can it be done? Yes, depending upon the structure over which a solid surface stone is installed and the methods used. We install solid surface shower walls regularly, but from an empty cavity which we build to meet all specific design and installation specifications, including the pan. A solid stone slab cannot be supported by the pan (it is not meant to support a slab wall). A slab wall is pinned and tied so it is self supported, not supported by a pan. This is a very complex installation. A LOT to consider. As one example, the thickness of your slab? 2cm. 3cm? (effects the weight load on the space). And I could go on. After you have carefully vetted the qualified tile contractor, have this conversation with them. If you question or want to clarify their recommendations, check back or seek professional advice from other qualified sources. Please consult with a professional onsite. Good luck with your project.

Those GRIF form bases look really cool! I like our Corian counters in the kitchen, I think Corian would be an excellent choice for a shower base. We installed a Swanstone base in our shower about 3 years ago. It has been very easy to maintain, but I guess I can't speak to long-term durability. The shower is used every day, currently by 4 people while we remodel the other bathroom. I'd say it still looks as nice, today, as it did when we installed it. I like the raised non-slips more than etched (our new Kohler Villager cast iron tub in the other bathroom has etched nonslips and they feel like chalkboard to me -- I'll probably stick the bathtub mat over them when the remodel is done). I'd go with Swanstone again if I had to make the choice. We also have the Swanstone solid surface shower niche, and that is a piece of cake to maintain.

Pete summarized the main points nicely, though I'd disagree that solid surface pans are all ugly. Plain, perhaps, but I don't think they necessarily detract from the look of a beautifully tiled shower. But in the end, aesthetics are a personal opinion, so only you can decide if it matters to you. One more thing no one mentioned: pre-fabs are idiot-proof. If tiled floors (and all the stuff that goes underneath) are not installed correctly, you can end up with a mess on your hands. But you don't often see GW horror stories entitled "my contractor screwed up my solid base shower!" :-) My sister has a tiled shower floor and complains of discolored grout. That's what drove me initially to do a solid surface pan. Ease of install and idiot-proofness were bonuses for this DIY-er. And I like it fine. We're done with all the bathrooms in our house, but now that I'm much more informed about shower construction, I'm likely to try a fully tiled (and kerdi'd) shower in a future bathroom project, should it materialize someday.

With large format tile and the modified thinset, there was a pretty good chance that the thinset had not created a strong enough bond where the Kerdi would be damaged when the tile was removed. Without a doubt, float out the wall prior to continuing. A good foundation will improve your chances of success. I've used Versabond quite a bit over Kerdi, but I don't use it with large format tile because the tiles are so large. Modified thinsets need air exposure to completely dry and develop a complete bond. Thinset sandwiched between a large format tile and Kerdi will not see much air, especially the thinset away from the perimeter of the tile. If you're using Versabond, I'm guessing you bought it at Home Depot? Custom's unmodified thinset is Customblend. I'm not a big fan of Customblend right out of the bag, but if you have to use it, I'd recommend picking up a bag of portland cement and adding a margin trowel or two of portland cement to each batch of Customblend thinset that you mix up to fortify it a bit. Definitely change to a larger notched trowel to apply thinset to the wall, and definitely burn in and back butter the tile prior to setting it. It will help immensely with coverage and adhesion. The gap under the bottom row of tile? It depends on how inconsistent the floor/wall junction is as you go around the room. If it's wonky, with the floor already tiled? I'll toss out rough numbers for this example: Let's say your tiles are 16" square and you had a 3/8" gap in some spots between the bottom of the wall tile and the top of the floor tile, and in other spots they touched. Your best bet may be to strike a level line across the four shower walls about 15-5/8" above the highest spot on the perimeter of the floor. With a 3/8" variance in elevation around the perimeter of the floor, that line will be 16" above the lowest spot on the perimeter of the floor. You then scribe the bottom edge of each tile so it conforms to the floor tile, so when the tile is set in place the top edge of the tile will be on the line you drew on the walls. Some tiles may fit without having to be cut at all. Others may have up to 3/8" taken off their bottoms. Others may vary, you'll have to trim a bit here, a bit more there, to follow the contour of the pebble floor tile. A pain? For sure. But that'll solve the uneveness of the wall-floor intersection, and with the top edge of your bottom course of wall tile now being spot on perfect level around the entire shower, you've created the proper foundation upon which to tile the upper walls. An overall generic lesson? First thing I do in any shower is fix the framing. With square and plumb framing I get square, plumb, and flat backer board and plumb and square wall corners. With good backer board I get a good tile installation. Fight the framing at the start and that's the only battle you'll have to fight. Everything else will follow smoothly. Good luck!