Forming dome (Refractory)

[sonomacast]

I have now formed the dome of my oven using sand but I'd like to finish it in Plaster, What can I use to seal and hold the sand in place? I was thinking of paper mache? What other materials can I use?

[david s]

I used strips of wet newspaper over the sand, then cast onto that. It gives you a pretty good surface on the inside of the casting and any newspaper left behind will burn away. I think you'll have a hard time breaking a plaster crust away from the inside of tHe dome no matter how much release agent you use.

[sonomacast]

Striking the dome will not be a problem as is will be segmented into 5 equal pieces and one large piece. I have mold release agent which we use at work but I see the peri and doka type formwork pans have a (Greasy) wax coating on them which seems to last at least 2 pours So I was thinking of using the wax and release agent. The door arch will be difficult to strike from the form I know but hey, that's what I do for a living, Just hope I don't destroy the form whilst removing the concrete.

[david s]

"Just hope I don't destroy the form whilst removing the concrete." Sounds like you want to reuse your mould, in which case a plaster crust is highly unlikely to survive. Make a fibreglass mould if you want to do more than one dome.