Anyone know what this is?

[finlaand]

Hi was going to see if the single storey extension had a batten wall, and turns out behind the plaster wall is c70mm of this crumbly stuff ,black weird stuff, any ideas? Kf it does insulation purpose I'll leave and save me replacing all with celetox. Else put 50mm celetox on top of plaster, then new plasterboard.

 

[finlaand]

If helps this extension was done in 1970.

 

[Mottie]

Cinder block/ Breeze block.

 

[finlaand]

Ok thanks, I'll guess it's celotex over plasterboard time then which is good as bought it already, thanks.