I tiled over the tile in my shower, you can do it if your subfloor is great. Mine was cement, I think yours is too?
The tile in my bathrooms was tile directly over vinyl, directly on plywood. Wait, there was a sheet of paper in there somewhere, I think between the vinyl and tile. Hmf, Anyway it lasted since they did it in 1973. The grout was busted out in some spots, but I think there was a leaky toilet involved in there.
You can get away with more flex using a mosaic tile because you can't get the leverage on them to break tiles. You'll break the grout eventually if it's bouncy, but that's not bad to fix every 10 years when it happens. I wouldn't do this in your entranceway where it gets a lot of traffic, but really how much walking around is going to happen in your bathroom? And 2 fatless cyclists? Mandi on Pearl's shoulders would hardly flex even a terrible floor.
I told Pearl via SMS today that I'm done with my tile stuff for at least a month. You are welcome to my tile nippers, tile cutter, and tile saw. And my grout float and sponge though they might need to be replaced soon.
My tile saw is a $50 lowes piece of crap. It cuts great, but adjusting the size is a pain in the dick. The fence that slides left and right to set the size just kinda floats and you lock it in with 2 thumb screws, one on the front and one on the back, it's just loose in there otherwise so you have to actually line up the front of the fence, and then the back, or the fence will be crooked. It's an extra annoying step, I'm sure a $500 tile saw works super fast and straight but this gets the job done. Plus you don't have to worry about renting it extra days. I had like 30 different size cuts I had to make between putting in that shower niche and that weird shower stall I have, you might only have to set the size on it a couple times and it's not a big deal. It's a wet saw too.
ANYWAY you are welcome to it. But I'm going to tile my basement sometime this winter so I'll need it back at some point.
The tile cutter works great, have to use that on mosaic tiles and I ened up using it for 1's and 2's of tile cuts so I didn't have to set the fence on the saw. It's super fast to use too.
Oh I have a square notched trowel and a v notch trowel.