I'm looking for some advice on repairing an old plaster wall after a water issue. I scraped the bubbling paint/plaster but found the underlying plaster to be damp and very soft so I chipped away as much as I could (see pics). Before I make unnecessary mistakes I'm looking for some advice on re-plastering over the brown plaster, which itself has many thin cracks. Is a screen necessary? Could I use joint compound or must it be plaster? Can I seal the brown later so that water doesn't leak through the cracks (if the roof repair is ineffective) or would this prevent new plaster from adhering?