This area of the wall is where the old heating stove used to connect into the main chimney stack. There was quite a bit of damaged plaster here.
In order to repair it, we first removed all of the loose, crumbling, or unstable old plaster all of the way down to the lath.
Then, we screwed pieces of drywall to the lath to fill in the bigger areas. When applying the drywall pieces, it’s important to note that it needs to be slightly thinner than the old plaster. This allows for the drywall to be completely hidden under the new drywall compound.