After I left on Friday, the builders got on with making things go away.
With the mouldy and damp plasterboard removed, it becomes clearer that remodelling the room could work out quite well. The shower wall turns into a door that opens inwards and left, and the existing door is turned into a wall. Replace the oversized 1.2m double radiator with a 1400 x 400 vertical radiator in the middle of the interior wall to reclaim some wall space, put a soft chair in the corner by the proposed bathroom, add a futon and a chest of drawers, and it’d be a nice guest room.
The boarding up around the water tank is coming together too.
I also took out a bit of frustration on a wall – it sounded solid all the way until right next to the outside wall, where it turned hollow. So I poked it with a small pry-bar, and found bonding. 40 mm of bonding. Tapped the wall again, the hollow sounding bit has moved. Dig some more, hollow moves, dig some more, hollow moves. The entire stretch is bloody bonding. If we strip it all back, it’ll make the 1.4m high ledge in the third bedroom just that little bit wider, turning it into a nice bookcase base.