wall prep for tiling

[ahpotty]

I have drawn a blank on how to proceed with preparing surface for bathroom tiling. When some of the tiles were taken off to allow for the ceiling to be insulated internally (1854 construction outhouse single storey)
some of the previous plaster came off back to a tanking membrane. Behind this is the brick wall. the tanking membrane is not firm.

solutions I have rejected
I thought of tiling over the old tiles but they were of different thicknesses so the wall surface is uneven by 2-3mm where the tiles are and 5-6mm where new tiling will be going.

I thought of taking off all the tiling and getting the wall replastered - expensive and quite a wait until it dries for tiling maybe.

I thought of dot and dab plasterboard but how to install
I thought of marmox sheet but how to instal

Any ideas?

 

[stef99]

If you can't plaster, then dot and dab is your best bet.

Rip it all of so that no water gets down the back.

Batton it all out flat and make sure everything is level.

Reboard it with plaster board and fill the gaps.
Most people will recommend using the water proof plastrbaord.
If you are only half tiling the wall, you may need for it to be skimmed.

Re tile on top.