Hi all! We’re in a 1950s home with all cement walls (seriously!). The walls do have an older style of “drywall” over the cement walls (like a backing with thin layer of plaster. A Similar width of drywall). In the bathroom their was wall tile halfway up and shower tile that all matched. Sea-foam green. We’ve demoed the tile off the walls and a layer of mortar/mud or whatever they used to build the wall out and adhere the tile to is still on the walls. Any recommendations on:

1. How to remove down to smooth cement walls so we can build out with cement board (shower) and drywall for bathroom walls to prep for shower install.
2. Or cover with material over entire walls
   (upper and lower) to prep for shower install?
3. Any other recommendations??

Thanks!!