To hack off or not to hack off?

[oleoleole]

I need advice. This is a corner shower area in a 1910 cavity wall building. What would you do with the plaster - hack it off, or attempt a repair? The older plaster on the right wall is coming away where bricks have been revealed, but I wouldn't fancy hacking off the cementitious plaster on the left (where an old window has been blocked up).

Plan, for context, will be to put extruded foam (Kerdi/Wedi) board over the top. Apparently this can be dot-and-dabbed to bare brick/block but if plaster is repaired then it needs to be primed and fixed it with tile adhesive. Experts, which would you choose?

 

[mcprinter]

DIYer
I used Delta Foam Board direct onto 1930s Brick Wall after removing the old Plaster.
Primed the Wall. Stuck on with Tile Adhesive. Also screwed and used Tile Backer Washers.
Taped the Joints and tanked to whole lot.

I fitted Wall Panels rather than Tiling.

You may find some Tradesmen saying Standard Plasterboard is fine. Probably is if the Tiling/Sealing is absolutely spot on.
To me, it makes sense to spend a little more on fully waterproof Board and Tanking.

 

[oldbutnotdead]

1910 cavity walls? Posh .
If the plaster is loose or sounds hollow then chop it off, if it's solid then leave it be (unless you need the space)