Question on shower pan mosaics: When using a bonded drain flange, I have found that many times the drain grate is taller/thicker than the mosaic tile. For the pan to drain properly, the tiles have to be ever so slightly above that grate. However, if you put down the amount of mortar needed to hold the tile in place, the tiles rest below the rim of the grate.
We are not supposed to build up with thinset, but what else are we able to do in order to get the tile to the correct height? I have not seen anything in the manual that addresses this.
You are correct – I would not build up with thinset.
I suggest your best option is to speak to the drain manufacturer to ask if they have alternative grates with lower profiles for thinner tile.
Assuming you are using foam pans, I am not aware of any other material that would make sense to add on top of the entire pan to build up height. If making mud pans, you can likely correct for the height difference.
If making mud pans – and you want to stick with surface-applied membrane – you could switch to clamping ring drain using the divot method. This method is shown in TCNA Handbook Method B422. It might help you resolve the finished tile to drain height difference for thinner tiles.