Renovating my son's apartment, a building from '48. I've removed a non-load-bearing interior wall. There are marks left on the ceiling but also on the floor. The ceiling is made of concrete with some type of 1 cm thick cement plaster - see image. On top of that, a few millimeters of darker plaster. Edges and the rest of the ceiling are in good condition, nothing else is loose. The area to be repaired/filled is about 3 m x 10 cm wide and 1 cm deep. The question is how do I fill in the ceiling and with what type of plaster, and do I need some kind of primer? Everything seems to hold quite well anyway. As for the floor, it's about the same, the marks from the old wall are about 10 cm wide and one centimeter deep and about 3 meters long. Fill with fine concrete? Gypsum plaster? Mortar? What the heck should I use, and how do I get a good grip on the ceiling and make it smooth and nice?
