I have an internal wall in a 1980 flat conversion that appears to be
concrete sheets with breeze block colour/style material sandwiched
between. On hardness; I can't scratch or crush it with a fingernail
but can comfortably eat into it with an old screwdriver. Total wall
thickness is about 160mm or so. After chasing a channel the 1cm
concrete layer is very consistent and doesn't look to be plastered on
to the internal material, it looks more like a bonded sheet.

Can anyone identify what type of wall this is? Was it a typical build
material for creating internal walls in the late 70's, early 80's?

I ask the question because I need to secure fixings into it to hang a
20kg glass showerscreen which provides 4 fixing points along the hinge
on which the glass hangs.

I am almost tempted to run bolts right through the wall and use sunken
nuts and washers on the opposite side - but that might be overkill,
and fiddling about with threaded rods might be a pain.

What would people here recommend?