When I previously drilled into walls in the same property, I thought it was lecablock behind the plaster, because the drill dust was gray-black. But when I removed a piece of a wall in my own place, it didn't look like lecablock at all. There are no traces of any leca beads, but it is a dark gray uneven coarse mass with sporadic jet black small lumps resembling melted black glass, and the occasional air pocket. It's a real pain to attach things to. What is this called, and what is it made of?
Spontaneously, I would say lightweight concrete, but it's hard to tell from the pictures. Can you provide us with a close-up with some object for reference? It is quite unusual, however, for lightweight concrete that isn't relatively "fine" in structure and that lacks uniformly sized air bubbles. Even lightweight concrete factories had bad days in the past though. When is the building from?
It is from 1946. Lightweight concrete can be glimpsed at the bottom edge of the second image, and it is both fine and even in structure. The image is a bit too bright. I cannot take any more pictures as all the demolition material has been removed and the remaining surfaces are obstructed. A couple of people who live in properties from the same era mention slag plates. And it probably looks like a by-product such as slag...
