extended curing...no cooldown

[ThermoJax]

My oven was dried out using a electric skillet set to 225 for a week and then 2 weeks with an abnormally dry time here in north florida , then 4 days with the skillet set for 400 and the door plugged up with insulation. Then, things went quick. The chimney got built, the dome wrapped and the first fire started. I put one of those long thermometers that are meant to go into the meat while in an oven and snake its was outside the oven to a readout diplay, into the oven on the opposite side of the fire, and started small, twigs etc, then after a few hours, I cut up dried firewood (cherry) on my chopsaw into thirds and added those. My fire has been going almost constantly for 2 1/2 days now. It has gone out whilst I have been sleeping at night, but I get up at 6 am and start it again. My thermo probe thing says that even in the morning, the floor is still around 240, and after day one, it was around 350. Today, it seems to be around 280 to 300. I have alot of black from about 3 inches and up from the floor, and I assume that only "scary fire" will burn off the soot.

Do I need to let it cool down? Way down. Is the cycling really needed, or would a week of solid fire be helpfull? I am self employed, and this is my baby, so I am willing to camp out next to the thing if needed. I am going out now to add another 1/3 log to the fire, and maybe boost the heat with my wifes blow dryer which I have taken temporarily. Any responses are much appreciated.

Tom

(also, I wish I had used 4 inches of the insblock 19 under the floor, instead of 2, as my hand up under the 4 inch concrete pad says that the concrete is more than warm, but maybe not hot) I hope the pad doesn't spall and fall apart, but if it does, cay sara sara.

[SCChris]

Re: extended curing...no cooldown

Tom the curing is going to push a lot of steam out from the support base, under the oven floor. Once the concrete drys out a bit I think you'll find that you're ok. These ovens seem to settle in after about 15 or so good burns, so my bet is that after the formal "Hell Fire" the curing goes on for a while.

Chris

[dmun]

Re: extended curing...no cooldown

I wish I had used 4 inches of the insblock 19 under the floor, instead of 2, as my hand up under the 4 inch concrete pad says that the concrete is more than warm

You'll be fine. Everything is still wet. I have 2 1/2 inches of insblock under my floor, and my slab hardly gets warm.

[SCChris]

Re: extended curing...no cooldown

Tom,

I didn't answer your question about cool down. It's my opinion that a cool down during curing isn't really as necessary as some might feel. I kept my curing burns very long and steady and closed up the doorway between burns to maintain the higher temps. I feel it's about bringing up the temp slowly and maintaining the temp to get the water moving and keep it moving out of the oven

There are several things happening during curing, Drying and Thermal expansion are the 2 biggies. What we don’t want to have happen is for the existing water in the oven to flash to steam. The volume that steam occupies is somewhere around 1500 times what water occupies so when water flashes into steam and the space constrains the expansion something has to give. In our WFO world the oven structure cracks.

Another source of cracking is the thermal expansion of the structure. If the whole oven is heated evenly the stress cracking is minimized. As long as everything grows at about the same rate the cracking is minimal, not eliminated but minimized. It’s important to point out that the mortar isn’t going to grow and shrink at the same rate that the bricks will, it’ll be close, but it won’t be the same. During cool down the oven is more likely to be more even throughout than on the heating cycle so less cracking will happen on this part of the cycle. This is my opinion..

Spalling is another thing altogether and it relates to the minerals in the brick failing due to the high heat. The presence or absence of these minerals in the raw clay is the difference between a firebrick and standard clay brick. This spalling happens at the higher WFO temperatures and is seen on the brick surface in the high heat areas. A similar sort of thing happens on bricks that have frost damage.

Chris

[Neil2]

Re: extended curing...no cooldown

I suggest you cycle the oven with a cool down between firings. This will stress the oven as it would be during normal usage and give you the opportunity to fix any serious structural cracking that occurs.

Spalling is very rare and generally indicates a flaw in the brick.

[ThermoJax]

Re: extended curing...no cooldown

Well, not being sure about curing with insulation or without, I have wrapped the dome with inswool, and then built a structure around and over it, making it impossible to see the outside of the dome for any cracks. However, I can see the inside of the oven, and there is no evidence of cracks. Last night, I let the fire go out, and did not relight until 2 pm today. I have a low level fire going, and some nice coals. I have a buddy coming over at 6 for pizza, and plan to ramp it up before then.

[Neil2]

Re: extended curing...no cooldown

"Well, not being sure about curing with insulation or without,"

Some have done it before and some after insulating. I don't think it makes much difference.