Check out this
https://www.thisoldhouse.com/ideas/plaster-repair-made-easier
Will give you some history on plaster repair.
As for plaster, there were two types. The older plaster installed over thin wood lath, and had horse hair mixed in with it!
Then later, they dropped the LP for blue board, and floated with plaster.
Repair Your Lath
The lath is a thin, narrow strip of a straight grained material, such as wood or metal. Repair your lath first. Nail 1.5 inch wood strips over the frame and leave a space of 1/4 inch between each strip. Remove remaining pieces of damaged wall and debris.
The Three-Coat Plaster Technique
The three-coat plaster technique begins two rough coats of a combination of lime or gypsum, fiber, aggregate and water applied onto the lath to form the wall base. This is called the "scratch coat." It is applied at a thickness of 3/8 inch and scratched with a comb. The second rough coat, called the "brown coat" is made of the same mixture, apply in the same way, but its finish is smooth, not scratched. The final coat is called the "white coat" and it is made of plaster combined with lime or a store-bought comparable product, apply in 1/8 inch thick layers for a hard, even finish.
It's All In the Mix
Professionals tend to mix their own plaster out of a combination of putty, water, lime and comparable materials, but this is truly an art. Instead, consider buying a prepared plaster material from your local home improvement store. Use a mixing tub to combine the base material with water, until your plaster has a mud-like consistency. Mix the whole bag for large jobs but only the amount you need for smaller repairs.
Apply the Mix
Apply the plaster using a mud pan, collecting it onto the pan rim and transferring it to the wall, or transfer directly from the mixing tub. Fill in the gaps between the wood strips of the lath. Begin at a corner and push the plaster material from the pan onto the lath. Apply the first coat, scratch it, and let it dry before applying the second coat. Build up the coats to fill in empty spaces. Allow the plaster to dry overnight before proceeding to the third coat.
Finishing Touches
Once the first two layers have hardened, apply the white coat. Use a setting-type joint compound for this layer, which you can purchase. Plaster can also be used, but it can set before it has been applied so it must be mixed with precision to avoid cracking. Mix one part water to two parts plaster a little at a time until you have a mixture that holds its shape when upside down on the joint knife.
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