block type

We've undertaken a DIY project to soundproof an upstairs bedroom party wall shared with our noisy neighbours. There's a window on the perpendicular wall so there's only approx 70mm before the party wall would hit the windowsill which limited options. We decided on resilience bars, sbx boards...

Early eighties build, inner leaf and inner wall blocks a sort of blue/grey slate colour, not aerated thermalite type (a similar size though). Whilst they're not as hard as modern concrete blocks, they're still quite dense, and they have inclusions, sometimes white, other colours too. What are...