Tiling bathroom floor

[GC Newbie]

I am about to redo my bathroom which involves installing a walk-in shower, re-positioning a bath and sink, and tiling the floor and walls.

It is a Victorian house and I think it would be best to remove the floorboards (instead of over ply) and replace with 18mm ORB. This will give me easy access to install new waste pipes, give me a flatter surface for tiling over and avoid creating a step into the bathroom.

I have 2 concerns... Will this provide a secure enough surface to lay tiles? The bathroom has been extended by removing an original wall and now has a stud wall perpendicular to the existing floorboards. Will I need to secure the floor boards I cut in the adjacent room?

Many thanks and any extra advice would be great.

[wine~o]

Osb I think you meant. You'd do better using decent quality 18 mm ply, deffo go for a good quality tile addy as well, mapeii flexi for instance.