Digging into the sewer pipes in an old 1930s house before replacement. I'm not an expert on materials and can't quite figure out what they've used as the top layer of the floor. A thin layer of stone and gravel, then some fairly porous mortar, and then something relatively hard but brittle that leaves sharp edges.
Attaching some pictures - can anyone clarify for a complete layman?
I think it is cast in two stages, first a rough casting and then a thinner casting in concrete with smaller/finer aggregates in it.