I am tiling a floor where the center of the room will have a decorative rectangular mosaic piece. That piece will be framed with border tiles. The rest of the floor will be ceramic tile. My problem is that the mosaic will be thinner than field tiles, perhaps by 1/8" and it is possible that, depending on tile choice, the border tiles may be slightly thinner than the field tiles but thicker than the mosaic. I am wondering what the best way to handle this is.
I will be putting down cement board and I was thinking that, before laying the board I would put down a spacer where the mosaic is, and if needed, for the border tiles. That way, when I installed the cement board, the surface would beh uneven but when the tiles were installed they would all be at the same level. A possible problem I see is that the cement board joints would align with the joints between the different tile types. Is this an issue? How are installation problems like this usually handled?
The photo shows the mosaic and some of the other tiles we are considering.