Plaster of Paris...

[ronyon]

Has anyone cast a riser and/or burn tunnel out of plaster of paris?
It is used as a refractory for casting non-ferrous metals.
I started wondering about this after coming accross a gypsum/perlite plaster while searching for perlite.
Seems gypsum itself can't take much heat, but the simular plaster of paris can
It is also noted for it's low heat transfer.
I am thinking it may be easily abraded .
So how does a mix of plaster of paris, perlite and fiberglass fibers sound?

[oboblomov]

Wikipedia says this about Plaster of Paris:

Gypsum plaster (plaster of Paris)

Gypsum plaster, or plaster of Paris, is produced by heating gypsum to about 300 °F (150 °C):[2]

2CaSO4·2H2O + Heat → 2CaSO4·½H2O + 3H2O (released as steam).

When the dry plaster powder is mixed with water, it re-forms into gypsum. The setting of unmodified plaster starts about 10 minutes after mixing and is complete in about 45 minutes; but not fully set for 72 hours.[3] If plaster or gypsum is heated above 392°F (120°C), anhydrite is formed, which will also re-form as gypsum if mixed with water.[4]


I would guess that, when heated, a P of P casting (once again gypsum) would crumble. Don't have any experience, however.

Obob

[ronyon]

www.bronzecasting.co.uk/4_investment/plastergrog_4.html


Different material than gypsum.
Related but different.