STILL the same ****en idiot "wanna be know it all" you'll always portrayed your self to be" Stick to General contracting and let the PROFESSIONALS answer this question Philamina
Hit it with a quick set powder mud like CGC sheetrock 90 or the USA equilivant, , level it with a coat of mud, then skim it wih a thin coat of mud . Lightly Sand in between coats by the way.
While Phil is "trying" to answer your question, he hasen';t a ****en clue.
Once the paper is exposed, there's really nothing you can do but build it up to surface level.
IF he ACTUALLY knew what he was talking about he would see from your pic, the gypsum ISNT expoced, even if it was, it wouldn't matter.
WHY??
Simple, today's "mud" products are calcium based, as opposed to "pre" 1960 Morter based plaster products, which would require a bonding agent, and multiple bonding coats
.
Prime, then cover it with a "wiz roller" of finish, second coat it with the same technique, then finish the whole wall.
depending on your choice of finish I'd recommend Benjamin Moore "Ben" series, or Aura.
IF you were to follow Philimeanas advice you'd be re-gyprocking the whole dam wall. But then general contractors rarley know what the **** is going on anyways
Any further questions feel free to ask me through email
jeffchildsceilingmaster@gmail.com