This area of the wall had what appeared to be cement over the area where the heat duct is. It seems to be from when the central heat was installed because it’s in every area where there are heat ducts running in the walls. My guess is when they tore open the plaster walls to install the ducts, they used this cement type of stuff to patch up the holes rather than replastering. It’s not a very smooth application, so we’re having to tear it all out to do the repairs correctly.
New lath installed.
Then a large piece of drywall was added to help reduce the amount of joint compound that will be needed.