Retro Insulating cavity wall With celotex.

So we're starting to do a bit to our 50's ex authority house. Smashing the granny out of a few internal and external walls.
One problem with the house in its current state is the build up of moisture around the walls near the windows and in the cold corners of the house cavity wall insulation was installed years and years ago before we moved in.
The upvc windows do need replacing. That's all for later posts....


My questions to your good selves is this, as we are dabbing 12.5mm board everywhere is it possible to first of all stick 25mm celotex to the walls with an acrillic adhesive then stick the gyproc to the insulation using a spray adhiesive and finishing off by drilling through the lot into the brickwork with a hammer fixing. My main concern is the possibility of condensation and mould build up between the brickwork and celotex.
The celotex will stick to the board with spray tried a little piece of this and placed a block to sandwich it. The Walls to be insulated are 75mm cavity walls.
I also have spoken the celotex technical department but left the call with more questions.

use thermal plaster board

I would do, but to achieve the same R values with it this way i would have to spend twice as much on a pre manufactured board.

I may be off the Mark here but can you insulate on the outside and render over that ?