Wall and floor prep - bathroom remodel

[Samosaurus]

Hello all,

After years of abuse, the bathroom needed an overhaul from top to bottom.

Out came the bath, sink and toilet. Corner bath still upside down in back garden....haven't got round to cutting it in quarters yet to take to the dump.

Toilet was never fixed to the floor 😆

Floor tiles came off relatively easy

Wall tiles were a b**** Hammer and bolster could not manage to get off the two layers of tiles stuck directly to plasterboard. 🥶
Hammer drill and chisel helped a lot but still was not an easy process.

Now I've come to the stage where :
1. T&G chipboard flooring needs replacing with 18mm ply - Current state of the T&G chipboard is unusable from water damage.
Do I go with 2.4m x 1220mm or 1.2m x 610mm boards?

2. Two walls have been plastered over cinder block -
Should I repair the walls with thistle hardwall, then fix concrete backer board or remove the plaster and fix concrete backer boards directly to cinder block?

3. Two stud walls have two layers of plasterboards....no idea why and i don't want to know either. The stud wall is quite thin. I've started to remove the damaged first later of plasterboard that's been stiuck to first layer with mortar....😩


Can I fix concrete backer board directly to the stud wall on top of the second layer of plasterboard or there's a better way of doing that?


Concrete Backer boards : 6mm on wall and floor. Any difference between all the brands out there or they do pretty much the same job?

I hope the pictures attached gives a better idea what I'm talking about.


Thank you for reading and any advice most welcome!


Sam

 

[Slippery]

1. T&G chipboard flooring needs replacing with 18mm ply - Current state of the T&G chipboard is unusable from water damage.
Do I go with 2.4m x 1220mm or 1.2m x 610mm boards?

Chipboard wants replacing with chipboard, same size (2.4x600), glue battens all around the perimeter to glue the edge of the new board down or it will squeak

2. Two walls have been plastered over cinder block -
Should I repair the walls with thistle hardwall, then fix concrete backer board or remove the plaster and fix concrete backer boards directly to cinder block?

I would just stick wedi(cement faced, not solid board) all over any rough surfaces

3. Two stud walls have two layers of plasterboards....no idea why and i don't want to know either. The stud wall is quite thin. I've started to remove the damaged first later of plasterboard that's been stuck to first layer with mortar....😩

Would it be just as easy to fit a new board? this is ready to set tiles after being primed or tanked if it's in a wet area.

As I said, I would prefer wedi boards to solid cement although if the floor has any spring, use those, screwed and glued to the subfloor.