Trowel size for 10mm thick stone mosaic - Tile Advice

[risotto]

Have a question that's been driving me crazy looking tirelessly online without any solution.

Basically, I'm laying 10mm thick stone mosaics over a wetroom floor. The drain is fixed into the tray so there is no depth adjustment there to align with the tiles. So I need a total height of 14-15mm to match the fixed drain height, so was hoping that using 10mm mosaics would allow me to only use 4mm of adhesive bed.

The problem though, which trowel do I use to guarantee 4mm of bed once the mosaic sheets are pushed into the adhesive? Everywhere I've searched they generally always recommend a 3-4mm notched trowel for mosaics but there's nothing specific to my situation where I need a little more to increase the height.

Any ideas would greatly help

 

[Dave]

Hi , what size are the mosaics.?

 

[risotto]

Hi , what size are the mosaics.?

Hi, the mosaics are small hexagonal, about 25 x 25mm on a 290 x 285mm sheet

 

[Dave]

What type of wet tray do you have ? , most advise against using small mosaics due to point loading.

 

[risotto]

What type of wet tray do you have ? , most advise against using small mosaics due to point loading.

It's this one Wet Room Kit 800 x 1200 Point Sirocco - https://wetroomsdesign.co.uk/walk-in-shower-tray-800-x-1200-point-sirocco#/77,thickness,20-mm/94,drain-position,offset

It was actually them that suggested small mosaics as the best to install. Since I'm doing, it also seemed like the easiest option than cutting down larger tiles to fit the tray gradient