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Old 07-22-2009, 03:54 AM
Rodneyf's Avatar
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Default Curing methods?

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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Last edited by Rodneyf; 07-22-2009 at 03:58 AM.
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Old 07-22-2009, 05:32 AM
david s's Avatar
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Default Re: Curing methods?

I think they are spot on. I use a gas burner to heat the oven slowly (24 hrs) to about 250C then go to wood fires and heat beads. You need a fair amount of energy, expended slowly to convert a lot of water to steam. eg How long would you have to boil a 5 gallon tin of water to boil it dry ?
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Old 07-22-2009, 08:12 PM
MK1 MK1 is offline
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I'll be using this schedule and technique tomorrow, if it doesn't rain! I'll let you know how it works out. I fairly dread cracks. Don't be careful.

Mark
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Old 07-22-2009, 11:02 PM
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Default Re: Curing methods?

Mark, that sounds like you are about three weeks in front of me so I am really interested in hearing about your results, keep us posted.
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Old 07-23-2009, 07:32 PM
MK1 MK1 is offline
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Well, it rained on and off all day but Saturday looks possible. I have included pictures of my "heat stick". I used a few flare fittings and a 3' black iron pipe. I also have a heat shield for above the burner to disperse the flames.

Mark
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Old 07-24-2009, 12:44 AM
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Default Re: Curing methods?

Looks good and I hope we are on the right track but it all makes sense to me. The guy at Field furnace said that the render on the outside will get very hot during curing but will actually cool as the oven dries out during the process, he also said if you see steam you are going too fast and to just knock down the heat a little. Good luck.

A couple of pics of where I'm at right now.
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Old 07-24-2009, 04:45 AM
MK1 MK1 is offline
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Rodney,
That's an important tip, thanks. I assume the outer render gets hot because the vapor is going into the insulation as well as up the chimney. I incorporated a stainless vapor barrier so I don't think my insulation will heat up much.
Your workmanship looks excellent. That top plug makes me think you might have a large core bit or you're damn patient with the grinder.

Mark
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Old 07-25-2009, 02:07 AM
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Grinder old son,grinder! It didn't take long actualy I just did a rough cut with the saw then made the plug by grinding it down to size. When is the curing happening?
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Old 07-25-2009, 04:17 AM
MK1 MK1 is offline
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Today. I'll let you know how it turns out.

Mark
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Old 07-27-2009, 05:36 AM
MK1 MK1 is offline
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Rodney, it was a longer process than anticipated, but worked like a charm. Driving out the moisture at the 200c stage took a full 24 hours. I have 1.5" of refractory mortar on the outside of my bricks and I believe that was the never ending source. I was up every hour or so over night, but I could have just let the propane hold it at 200c and slept a full 6.
After the 200c stage I started shoveling in the heat beads for the 50c/hr ramp to a bit above normal operating temp. I used about 30-35lbs of propane for the first 30 hours and then 120lbs charcoal briquettes (heat beads) for the final ramp and cure at 1100 f. I haven't found any cracks so far. I don't have my metal dome covering the kaowool yet, and that was a good thing. I would advise you let an opening for vapor to escape because the moisture goes both ways.
My son helped the whole time and made a batch of bread for on the way down after we raked the ash.
We put the bread in at 420f hearth temp, at that was just a little low, (playing it safe) it turned out fantastic. I've never had good spring in a regular oven, but these loaves almost doubled.
I'm still a little dotty from the last 2 days so I might be forgetting a few minor details.
We had some rain, thus the comical rig over the oven.
This is a fantastic method of curing. Thanks.

Mark
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Last edited by MK1; 07-27-2009 at 05:41 AM.
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