Plaster

Plaster is a wetted solid, typically applied to uneven surfaces to smooth them or provide a good surface for paint or other treatment. It can also provide some weatherproofing.

Production

Lime Plaster

1. Gather 2-3 units by mass calcium oxide
2. Gather 1 unity by mass sand
3. Mix well
4. Dampen slightly (just enough to make the mixture spreadable)

   Check: The mixture should heat up

5. The mixture is lime plaster. It will "set" over the next few hours-days, depending on thickness of the plaster layer, airflow, and humidity.

Gypsum Plaster

Plaster is a partially dehydrated form of gypsum: 2CaSO₄•H₂O. Fully dehydrated gypsum, calcium sulfate can also be used, but the wetting and setting times are much longer.

1. Gather gypsum
2. Produce calcium sulfate "anhydrite" by heating gypsum over 150°C but below 180°C

   CaSO₄•2H₂O(s)

   {

   →

   150-180°C}

   CaSO₄(s) + 2 H₂O(v)

3. Shortly before usage, mix the anhydrite with water to produce a thick paste.

   Check: The mixture should heat up

4. The mixture is gypsum plaster. It will "set" in 45 minutes or so.

See Also

• mortar