Plasterboard in bathroom

[lost_diyer]

I’m renovating my bathroom and installing tile backer board on several walls where tiles were removed. These walls are in and around the shower.

There are two other adjoining walls with moisture resistant plasterboard. Should I remove the plasterboard from these walls as well, or can I leave it and tile over it?

If I were to keep MR plasterboard, would I need to sand down the paint before sticking tiles to them?

The tiles I’m using are large 1200 x 600 x 8mm.

 

[Mark DM]

Tiles were often put over just regular plasterboard years ago but any movement or leaks usually ended in tears. I would ensure that hardibacker goes onto all the wall areas within the shower area. If needed you can cut plasterboard back to a joint to achieve this. Any painted surfaces need to be deeply scored/ paint removed as much as possible to achieve a good bond. Using a SBR primer mix and tiling before it dries will also improve the bond.
I always scrim all the hardibacker joints including the internal corners with adhesive and allow to set before tiling. Make sure the backer boards are really well screwed and fixed to the substrate . No movement... no cracks.
Tiling over plasterboard outside of the wet areas should be fine as long as thoroughly prepared.