
70s apartment. Previously popcorn ceilings, now bare concrete. We want to paint the walls and leave the ceiling bare, but around the edges is this thick layer of black stuff... Maybe waterproof barrier? I Tried cutting some of it back and then wire brushing

the residual black tar like stuff off of the ceiling but it doesn't come off very easily.
We need to find a solution to either;
Have the stuff removed so the roof is back to bare concrete or
Can we paint over it and effectively have some kind of painted cornice