From the photo it appears that there are two (2 ) finish coats which would indicate that it has been skim coated at some time.
Is this Plaster applied over wood Lath?
As for repair using the Big Wally or Plaster Magic products the method works very well. If you have a small area to repair that the small package of three tubes will cover it is about $ 150.00.
If you have a large area research this article
Morgan W. Phillips formulations APT vol. XII No. 2 1980
The adhesive formula for unfilled is the same as the Big Wally's only you will be mixing your own it will be cheaper but you may not find all the ingredients locally.
If you want to by pass all the proven methods just use Elmer's Glue as you would the Big Wally product along with the plaster washers.
You would save $$$ by just removing the damaged plaster & applying a replacement plaster product with a finish to match the existing.
WHAT PART OF THE WORLD ARE YOU LOCATED?
Is this Plaster applied over wood Lath?
As for repair using the Big Wally or Plaster Magic products the method works very well. If you have a small area to repair that the small package of three tubes will cover it is about $ 150.00.
If you have a large area research this article
Morgan W. Phillips formulations APT vol. XII No. 2 1980
The adhesive formula for unfilled is the same as the Big Wally's only you will be mixing your own it will be cheaper but you may not find all the ingredients locally.
If you want to by pass all the proven methods just use Elmer's Glue as you would the Big Wally product along with the plaster washers.
You would save $$$ by just removing the damaged plaster & applying a replacement plaster product with a finish to match the existing.
WHAT PART OF THE WORLD ARE YOU LOCATED?