Plaster is a resource in ymir.
Plaster is used in the construction of buildings like Large House lvl 3.
Plaster is made in the Kiln by heating Limestone with either Charcoal or Coke.
To produce on unit of plaster you need 1.5 units of Limestone and one unit of Charcoal or Coke.
Plaster making is unlocked by the tech Plaster knowledge
A possible requirement to unlock plaster is having some limestone in your storage and two builers level 2.