Trowel size for 900x600x15 Limestone

[One Day]

I would use a 12mm square trowel and back butter the stone.

 

[Lakey]

Thanks for all your input.
I have varied from
12mm on the floor 6mm on tile to
12mm on the floor 12mm on tile as the stone isn't calibrated so varis by 4mm in thickness.
I'll post some pics when i'm done

 

[Time's Ran Out]

Anything that gives 100% coverage!

As I said !

 

[Simon Dale]

What do you guys recommend for 900 x 600 x 15 Limestone going down on Ditra Duo?
10mm-12mm notched?

Many thanks

20mm and back butter with 20 mm 12 and a 10