So, how on earth would one go about fixing this wall?

>>1225323
Tear it down and start again

>>1225323
Let the wall win

>>1225323
Ignore it and post on /r9k/

Scrape off the loose plaster, sand, apply new top layer of plaster.

>>1225921
>Scrape off the loose plaster, sand, apply new top layer of plaster.

It could be old water stained concrete. At any rate, OP, think of it as art. If you know enough buzzwords, have a man bun and a few tasteful piercings, it will work and you'll have a partner with blue hair in no time.

>>1225925
>you'll have a partner with blue hair in no time.
brb. water staining ALL the walls