I had a long talk to the guys at Field Furnace in Sydney and they build ovens, kilns and furnaces. They said they always use heat beads ie; charcoal because they can take 8hrs to get the oven to 200C and hold it there for 1hr per 50mm of lining. That means that if we have a 100mm thick oven we should be looking at 8hrs to get to 200C and hold that for 2hrs. They say that you can then increase the temp by no more than 200C per/hr till you have reached the desired temp. The theory is that a fire no matter how small the fire, it will produce a flame that will lick the dome with 750C (the flame temp) and this heat will produce hairline cracks. I think that by doing it their way I should be able to keep more control over the temps and not get the heat up cool down cycle of several curing fires but instead get a slow, controlled release of moisture from the dome. They also said that this must be done after the insulation and any render has been finished so as to keep the oven heating evenly. I have included the heat up sheet they gave me and would love to know what the forums experts think of the idea.
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