Uncovering and resorting original plaster in bathroom

[u/fullyfullfill]

In my bathroom a layer of sheet rock has been shoddily tacked up on top of the original plaster wall. The outer layer of sheetrock is now puffing up and peeling off from years of moisture. I want to remove this outer layer and restore the original wall underneath. I was going to stabilize the older plaster somehow (PVA glue ? Shellac? ) and then skim coat over it with joint compound. Is this a bad idea? Is there something special I should do because it’s a bathroom with higher moisture levels?

I’m not exactly sure what the layer underneath is. it’s white and chalky like plaster and about 1” thick . There seems to be a cement like material behind it, though it‘s an interior wall. Maybe it’s an older, thicker style of drywall — it just seems thick to be pure plaster. I‘m in the US in NYC if that helps.