Gypsum Plaster

Gypsum Plaster was invented in the 1890s. Prior to this, lime plaster was the basis for most architectural plaster systems. Gypsum gained rapid adoption after its introduction to the market because it sets much quicker than lime plaster. It can also be formulated to be harder than natural hydraulic lime putty plasters, which can lead to lesser flexibility in a plaster system, but also greater strenght.

Gypsum is an evaporite sedimentary rock that is quarried all over the world. Gypsum is composed of hydrated calcium sulfate (CaSO₄ ⋅ 2H₂O). This means it forms crystals as water evaporates, leaving behind deposits. It is processed into plaster.

Gypsum plaster is used in a variety of ways, including plaster of paris or molding plaster for ornamentation, plaster base coats, finish coats, and even drywall.

Traditionally, as is most common in American plaster systems from the turn of the century to the middle of the 20th century, gypsum is used in plaster base coats for its strength, and is a gauging component in plaster finish coats.