Which adhesive is best to use?

[Qwerty13]

Hi

I am planning to fit natural stone 300x100 tiles on my bathroom upstairs onto P5 boards.
I have been told I should fit ditra matting.
I have a couple of bags of Mapei Keraflex Maxi S1 from a previous DYI job which I would like to use if possible. However, I cannot find anything online saying I can use this adhesive on P5 boards.

Could someone advise please?

Thanks

 

[Neil29679]

P5 boards need overboarded, ditra will only help with lateral movement. Cement board then s1 adhesive