Bathroom refit

Revamping my bathroom. Replacing the bath for a walk in shower.
Removed all existing tiles, only to discover that the old 1930s plaster has started to come off, back to the brick.
I've decided to remove the remaining old plaster, and reboard with aqua board for the shower area, and other boards for the less wet area's.

The main wall in question is a cold external North facing wall.

I am thinking of battening the wall and placing insulation between the wall and boarding.

Can I tile directly onto the boards without skimming?

 

yes