Started Curing today

[BradNSW]

7 days after dome completion we built the first fire. 6 hours at 275-320 degrees at the top of the dome.

We have NOT insulated the dome, so we can monitor for cracks...none today!

Outside temps of the top dome bricks was steady at 105-110 after the first hour and stayed there throughout the entire burn.

Will be cold (25 degrees) tonight in Colorado and maybe some snow. So, when the fire goes out, the dome will get a blanket and tarp cover.

Tomorrow will be 6 hours at 350-400 degrees.

[david s]

Firing an uninsulated oven is risky. There have been numerous reports of this creating damage. The reason is that the big difference in internal temperature and external temperature can create thermal shock. The problem is made worse in very cold weather. You might get away with it so good luck. Often micro cracking will not be visible, but lover time those tiny cracks can grow, just like a small crack in a windscreen.

[BradNSW]

I'm confident it will be fine. I've got a king-sized comforter over the dome, followed by a plastic tarp. Then, wrapped around the top of the square enclosure is another tarp, giving a good 1-2 foot of extra air insulation. Air temps will be in the mid-20s.

In the morning, the inside should still be over 100 (lots of thermal mass!!) and the outside probably 50-60. I'll post the actual measurements of the dome top and the outside temps tomorrow.

[Giovanni Rossi]

BradNSW , Just curious, what is your plan if you identify cracks?

[BradNSW]

Interesting results this AM. I took the two tarps and blanket off the dome and shot the bricks external and internal with the IR temp gauge:

Outside top of dome 79-80.
Outside middle of dome 79-80
Inside of dome top 79-82
Inside of dome middle 79-80

Seems the thermal mass totally equalized under just two tarps and a bed comforter as insulation. The thickness of the walls are 4.5" (1/2 a fire brick), so the dome has over 1500lbs of brick!

As soon as I started firing up this AM, the inside quickly heated up to 330-370
The outside (30 degrees ambient air temp) however was cooling for the first half hour. Brick external temps went as low as 65 before they started getting the internal heat.

End of the day, internal dome top had been around 400 for 6 hours and sides were 325-350 at the bottom course and 350-375 halfway up.
Outside the top of the dome got to 149. When the outside of the bricks got around 120, the mortar started showing "glistening" spots, which I assume was water/steam releasing from the mortar.

For Journeyman...small micro cracks....leave them.
Large structural cracks...stop and repair, let dry and restart curing.

No cracks of any size today, so tomorrow it goes to 500 degrees for 6 hours.

Will be interesting to see what the dome equalizes at tonight. My guess is between 90-95.

Photo show this morning with a trace of fresh snow and the tarps on the oven.

[david s]

Firing an uninsulated oven is risky. There have been numerous reports of this creating damage. The reason is that the big difference in internal temperature and external temperature can create thermal shock. The problem is made worse in very cold weather. You might get away with it so good luck. Often micro cracking will not be visible, but lover time those tiny cracks can grow, just like a small crack in a windscreen.

To explain the importance of damage caused by firing an uninsulated oven, go to youtube and search for "flue tiles and fire" (I can't attach it because it is Web locked). It demonstrates how thermal shock of the temperature differential between the inner and outer surfaces will crack the tile. Because a flue tile is far thinner than an oven dome the result is more marked, but the principle still applies and reports of damage to ovens that have been fired uninsulated is testament to its validity.

On temperature measurement, all methods have their pros and cons, but all oven owners rely less on gadgets preferring to use sight and feel after much experience.
For baking I like the small, reliable and cheap bimetal thermometers that read the air temperature inside the oven at the centre rather than the surface temperature of theinside chamber roof or walls. It is after all the reading of the air temperature at a given position in the oven that you want. Their downside is that you'll kill them if placed in the oven with fire around them, they top out at about 430 C (800 F) so generally use only for baking and roasting temps under 300 C. Also the base they are made with is ridiculously small. Handling a hot metal thermometer that has fallen over is literally a pain. I pop-rivet a slightly larger base to them.

The second pic shows the method used by the old Italian mummas and is highly reliable and a good party trick to impress your guests.The other method is to use your eyes to view where the soot has burned off. This happens once the temperature has reached 300C and the degree of "clearing" is a great indicator of higher oven temperatures.

A hand held to the outside of the oven is also a great indicator. For my ovens at the top on the outside the warmth can be just felt at the top after one hour of fire. If it feels hot then it means there is moisture in the insulation layers (because it conducts heat). After around 1.5 - 2 hrs the cosy warmth has spread down to the base on the outside and the whole of the oven interior will be white, which indicates it is ready for pizzas. Ovens with different designs, thicker or thinner walls and varying levels of insulation layers will no doubt produce slightly different results.

Another really useful indicator when roasting or baking is your sense of smell. When it's about 3/4 of the way to perfection the aroma coming from the oven tells you it's getting close. Apart from being pretty accurate it's also very tantalising.

The third pic is of my thermocouple on my kiln which has a probe inside a porcelain sleeve. The readout works on the principle that an electric current is generated when temperature heats two different metals. Because the temperature and voltage are directly proportional, the display is simply calibrated to temperature. More modern versions use an electronic, digital display that require batteries. Those that I've used have all stuffed up from between one and three years, so I prefer the old anologue one.

IR guns are useful, but only read the surface temperature, Thermometers in doors always seem to read significantly lower than the internal chamber temperature at the centre and the probe as well as its display is quite vulnerable to damage as the door is moved about a lot.

[BradNSW]

David/Giovanni,

You both have concerns about driving out the water/firing/curing without insulation. I completely hear and understand your concerns and the reasons behind them, especially in this cold Colorado weather.

This is my third oven (first in cold weather below 40). My questions:
1. How do you know if a covered/insulated dome cracks??
2. How do you deal with waterlogged insulation? In the morning, when I remove the blanket, it is soaking wet and the tarps are dripping water.

Tomorrow, I'll do an experiment.

1. I will measure the weight of my ceramic fiber insulating blanket.
2 I will put the insulating blanket over the dome and do the 500-degree firing.
3. After 6 hours, I will remove the blanket and:
a. See if the difference in internal and external surface temps are as significant as they were today without a blanket (400 inside and 150 outside). Which points to internal stress in each brick.
b. Weigh the blanket and see how much water it has absorbed.

If the internal and external temps are much closer together (ie: 500/300+) AND the blanket did NOT absorb a large amount of water (ie: the steam passed through it), I'll definitely keep on using the blanket.

David,

I've used the simple thermometer in your photo 1 in all my ovens, especially when roasting or baking breads. Never installed thermocouplers...just something to go wrong, but for sure valuable info. For pizza, I just fire till the bricks clear (700ish F/350ish C), then move the fire/embers to the non-cooking side and throw in the pies!!

I appreciate all your information and advice...we all put a lot of effort and $s into these ovens and we want to optimize their performance and not blow them apart when firing!!

[Giovanni Rossi]

David/Giovanni,

You both have concerns about driving out the water/firing/curing without insulation. I completely hear and understand your concerns and the reasons behind them, especially in this cold Colorado weather.

This is my third oven (first in cold weather below 40). My questions:
1. How do you know if a covered/insulated dome cracks??
2. How do you deal with waterlogged insulation? In the morning, when I remove the blanket, it is soaking wet and the tarps are dripping water.

I was simply asking you to document your thought process for new builder to learn from.

I was wondering if cracks developed how you would know if they were inevitable or if it was because of the thermal differential that david s often discusses.

And, what you planned to do about the cracks.

The refractory layers on my oven were quite dry bc of the seasonal changes I had to deal with by the time I was ready to push to higher temps. You can read the detail in my thread if you're interested.

Regarding wet insulation, I know David always recommends holding off on the final waterproof render until the insulation is truly dry.

I think it comes down to how quickly a builder wants to dry out the brick or cast layer. You can certainly get that layer dry without adding insulation as long as you go low and slow. Generally, with insulation in place, you can accomplish the drying process with escalating fires over about a week. It really is personal preference as long as the why, the how and the risks are understood.

[BradNSW]

Good news. This AM (32 ambient air temp), the oven inside was 150-160 degrees. Outer brick temps were 120-140.

The was very little moisture in the large comforter I was using to insulate and capture moisture during the evening.

I fired it up and the oven started acting more like a cured oven. Temps rose quickly and the outer surface temps rose fast too. This leads me to believe a large portion of the moisture in the outside mortar is out.

SO...I took David and Giovanni's advice. Threw on two insulating blankets and 6 bags of vermiculite.

It got up to the 500 degree temps quickly and is taking much less wood to maintain that temp.

Slow and steady today as I continue to squeeze out the remaining moisture.

[BradNSW]

600 degrees today. Woke up to blowing snow and 30' F (see photo 1).

By 9 the snow stopped, and temps were moving above freezing, so I uncovered and started the final 600 degree cure.

It's 10AM and I've got a nice fire going and internal temp is approaching 600. Will shut it down after a good long 5 hours at 600. Photo 2

[david s]

1. How do you know if a covered/insulated dome cracks??
2. How do you deal with waterlogged insulation? In the morning, when I remove the blanket, it is soaking wet and the tarps are dripping water.

Any cracks should be visible from the inside. Maybe one layer of blanket that can be removed to inspect the dome on the outside would be the solution, enough to prevent thermal shock at the same time as not locking too much ,oisture in. Sounds like you have it licked now.
We live in the tropics and get nearly all our rain in two months so drying by sun and wind is far easier. Your conditions must be so much harder to deal with especially as you have the additional problem of freezing.

[BradNSW]

Curing is complete....Pizza with the kids in two days.

After 6 hours at 600 degrees, I threw in two nice logs and got the fire going hot. Top 1/3 of the dome quickly cleared of char/soot and all looks great.

Thanks for everyones input and advice!