Making molds and casting in place

[TBM66]

I've been pondering making an oven for almost 2 years.

I've toyed with a variety of ideas and keep coming back to the idea of using readily available castable refractory concrete.

I've been sketching on some graph paper and think it would be relatively easy to create a dome and opening shaped mold using sheets of 1" insulating foam stacked and glued in diminishing diameters until the top is reached. One would then use a sander to create a smoothly shaped dome.

Presumably you would take the negative image created by the process above and create the outside of the mold.

Has anybody ever done something like this?

Any comments or suggestions? I have to believe the precast ovens are made in a similar process.

Thank you for your ideas.

TM

[muppety1]

Re: Making molds and casting in place

I have seen pics of earth ovens made using a former of wet sand, so maybe you could do the same with castable , the stuff I have used works like a thick mud that could be layereed up maybe ?

[david s]

Re: Making molds and casting in place

I think a mound of sand is a simpler way to go rather than the foam, but you need to cover it with wet newspaper or the castable refractory will stick to it, suck moisture from the castable and leave a rough surface with bits of sand stuck to it. Use 10% water in your sand castle mix to achieve the right consistency for building it. The other major problem with a one piece cast is that there are uneven stresses placed on the dome, with the top getting hotter first. This tends to create cracking, so the dome is better cast in a number of pieces which is more difficult. Also the castable refractory is difficult to work with because it goes off pretty quickly and is extremely temperature dependent, also quite expensive.