my co-op hired their people to put in a new ceiling and two feet of wall all the way around, in my bathroom (my neighbor had an overflow AGAIN). These people should be out of business. They did not attach the ceiling to any part of my shower wall. They were an inch off of level on some walls and the ceiling is wavy and off of level as well. I'm trying to remedy the situation myself as it's too complicated to get someone else in here to fix the damage. So what I did is remove a row of tiles, thinking that there was drywall behind them, and then I could cut part of the ceiling off and put a new one in (note the they didn't screw the corners into anything and didn't measure correctly). Unfortunately, this is not drywall. It's some sort of plastic mesh on front and back and... concrete? Does anyone know what this is? I can't tackle this project until I figure out the substance. The apartment was built in the mid-50s and has rock lath walls with metal. I"m thinking this plastic is newer? Any help would be appreciated. Thank you!
I suspect that was perfectly ordinary fiber-reinforced cementboard (durock or similar) with the thinset well-adhered to the surface before you removed the tile, and took the surface with it.
That appears to be consistent with multiple reports of durock being destroyed when removing tile from it, requiring replacing the backerboard as well as the tile.
e.g. this image from another DIY site, showing very similar mesh.
The maker does not appear to be proud of this feature, based on no images from "official" channels showing it.