Plaster Flashcards
1
Q
What is plaster made of?
A
> gypsum (sedimentary, CaSO4*2H2O)
2
Q
How is plaster made?
A
it’s ground to a powder and calcined (heat treated to DECOMPOSE to the desired product)at 160-175C to form a HEMIHYDRATE
3
Q
What do the dihydrate needles do in the plaster?
A
They form a network of porosity that draws water out of the ceramic suspension for slip casting when the mold is used
4
Q
What’s the effect of water content in slip casting molds?
A
higher water content = more open porosity in set mold, more absorptive mold for slip casting
5
Q
How is dry wall/sheet rock formed?
A
Mixing plaster with cellulose or glass fibers, a foaming agent (for porosity), mildew and fire-retardant additives. Mixed with water and set between heavy sheets of paper
