Stripping back walls for soundproofing

doveman

My flat suffers from terrible sound transmission from the neighbouring flats and I think the walls are breezeblock, which causes the sound to flank into all the walls. I'm thinking of stripping the walls in my bedroom as far back as possible so that I can then build independent stud walls to soundproof it.

There were a couple of spots where the plaster was cracked and falling off already, so I pulled them off to see what the wall underneath looks like.

This is the wall between my bedroom and living room:


It appears that under the plaster I've pulled off (you can see at the top right a piece left on to give you an idea of the thickness) there's more plaster (the light grey stuff) and then under that is breeze block (the dark grey stuff). That yellowish stuff at the bottom might just be discoloured breezeblock, as the dark grey stuff continues below it (which isn't obvious in the photo).

The plaster (light grey stuff) is about 4cm thick, so if it's the same on the bedroom side and the party wall between my flat and the neighbour's flat is the same, then after stripping the plaster off I'd only lose 12cm in total from building independent stud walls like this (using 50mm acoustic mineral wool they need roughly 100mm):
Wall Soundproofing Solution 4: Independent Stud Wall

I also had a look at my hallway wall (the other side of which is my kitchen):


Here it looks like there's a layer of plaster (orange arrow), then breezeblock (red arrow, I thought this was concrete block at first but I think there's just a bit of light-grey plaster on top of the dark-grey breezeblock that confused me), then some yellowish stuff, then brick. I guess there might be brick in the living room/bedroom wall too, so I need to remove more plaster from that to see the full cross-section.

Assuming the wall isn't load bearing, perhaps another option would be to cut a gap along the top so that it's no longer touching the ceiling and then fill that with something like rubber that won't transmit sound to/from the breezeblock wall? I guess I'd need to acoustically isolate it from the end walls as well to stop the sound flanking from them though and that might be tricky if it's supporting them.