Tile straight onto the boards, don’t prime unless the addy manufacturer recommends it, most don’t; never, ever use standard PVA as a tile primer. Use quality flexible trade cement addy/grout over all boards, tape joints & don’t let tile grout lines coincide with board joints.
If you need to plaster MR board it must be primed with Bond it.
If you need to plaster MR board it must be primed with Bond it.
