Schluter Kerdi-Board

[Possom]

As I have discovered that I have a local stockist of Schluter Kerdi-Board, given its reputation, I'm going to opt for that product to cover a bathroom stud wall which an overhead shower over a bath.

I was thinking of either putting up
a) 12 mm Gyproc SoundBloc plasterboard then attaching 12.5 mm Schluter Kerdi-Board, or alternatively
b) 19mm (or possibly 25mm) Kerdi-Board on its own

Just to try and reduce some sound from the overhead shower going through the stud wall to the main bedroom. I suppose an extra 7mm of Kerdi-Board would help reduce sound without the additional SoundBloc, though I haven't actually seen the Kerdi-Board product up close so I don't know how dense it is.

There would be acoustic Rockwool within the stud wall in any case.

Separately, can the 5mm thick Kerdi-Board be used under floor tiles on a marine ply floor?

 

[Possom]

I had a bathroom installer around and he said that even if putting up Schluter Kerdi-Board on the walls, as it's not much more expensive to additionally tank it with a paint-on tanking product he would do that.

I was wondering if there's any drawbacks to this? Perhaps Schluter Kerdi-Board wouldn't absorb a paint-on tanking product?