House from 1964 with cast intermediate floor. Currently renovating the basement and was going to repair damage in the ceiling. Started tearing down around the damage (about 50x50cm). It turned out to be Heraklith with hard plaster on it. The Heraklith was probably at the bottom of the casting form as I can't get a clean concrete surface; it's "jagged." It's about 20-25mm thick, so limited insulation, I think. I now want to fix what I started tearing down. Which mortar is most suitable to use that adheres well to the ceiling? I was thinking of gypsum plaster as the simplest solution. I also have cement mortar A, rendering mortar B, masonry mortar B, and masonry/plaster mortar C at home. I saw that there was EPS concrete/cement with insulating properties, but I don't know how it adheres to the ceiling and maybe it's excessive...
Scraped away the loose parts, vacuumed and then managed to put up a "chicken wire" somewhat. Had to mix Puts&Murbruk C KC50/50 rather loosely to get it to stick to the ceiling. Halfway through, I felt I might have chosen plaster instead, but I'm keeping my fingers crossed that it works with C-bruk. It'll probably be two or three layers before I'm done.
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