What is the material in my wall?

[electro_elvis]

I was thinking of putting up some shelves in the hallway and I'm wondering what material the wall is made of.
While drilling, the following happens:
The first centimeter resembles plaster (white, brittle, and soft). Then it transitions to a slightly harder, still brittle, but jet-black material. The drilling dust is jet-black and very powdery. The material is very fine, think of chalk. It also stains a lot when wiping it away around the hole.

I was considering that it could be blåbetong, but the material doesn't have the blue-gray hue in it. Could it be some form of slate or slag plates?

Regards,
Jonas

 

[pinebar]

If the house is from the 1930s or 1940s, it is probably slag plates. They are also very uneven and full of small stones, so it can be difficult to drill without the drill veering to the side.

 

[electro_elvis]

Yes, it's a 1930s house. However, I found it very easy to drill into. But there might be different types of slaggplattor.