I'm planning a bathroom renovation, walk in wetroom housing the shower and bath.

I have a plan to tank the whole area as per normal over suitable substrate for a wetroom, but wanted to ask question about installing a thin layer of cement board on top adhered with thinset (?) like a large tile, joint it then polish a thin cement layer over the top to seal it from the water?

This style product https://youtu.be/1FTSJ1pGqOM

Sort of like moroccan tadelekt but polished cement?

Any thoughts?