I have a 270+ year old Federal Colonial, and the wall above the fireplace in the living room is badly cracked, and sections of the plaster have fallen.
Now this particular area, the plaster is adhered directly to the chimney structure. There are no wooden laths.
I know this must be horse hair reinforced lime plaster, its crumbly to the touch with a coarse consistency. Almost like sand. There is some other plaster work to be repaired such as cracked/loose ceiling in another room and some more wall areas that are cracked and loose.
My parents bought this house in the early 1970's, and did a restoration throughout their time living there but have since moved off to Maine and I am taking over the home.
I have attempted to consult some people on this repair but no one seems to actually understand the material the wall is made out of. One guy tried to know what he was talking about and told me to square up and cut out the area and put 3/8" sheet rock in and use some material that wasn't wall joint compound, but you had to mix it with water like plaster of paris.
Any ways, I am really hoping someone actually knows what to do. Maybe This Old House wants to come do a show on this repair!?!?
I have pictures but not enough posts to link them.