Another Minneapolis WFO

[Sixto]

Yes, I hope my week-2 pizzas are worthy of the ocassion! I just have to remember this is not about me and my projects, it's about my son and his bride, so I'll do the best I can and enjoy the outcome as if it were just another step in the process....

Speaking of process, today was a long, hot day of mixing and applying stucco to the gallery vault. 2 layers of AR Fiber Mesh are embedded into roughly 1" of homemade stucco - 4 parts mason sand, 1 part Portland Cement, 1 part Hydrated Lime, 1 part water and 1/3 part of Quickrete Concrete Fortifier for improved adhesion and water resistance. The whole thing is now covered in shrink-wrap, and I removed the plastic off the perlcrete to help it dry faster...some of the stuff I put-on 4 days ago was still wet.

Can't wait to start the drying fires.

[Sixto]

FIRE IN THE HOLE!

Today we successfully started the drying fires... Weather this morning is partly cloudy, dry, and about 60F.

• First order of business was to move the tent away, add the stainless flue extension, get some charcoal briquets white hot and heat up the chimney.
• Second, I tried spreading the coals around in smaller groups but that only got the dome to about 100F
• Next I moved all the coals to the center and added some kindling.... that got me to around 155F

• Finally, after adding even more dry kindling to the coals, I reached the temp goal for day 1 - around 200F at the top of the dome, and cooler below as I aimed the infrared thermometer around the inside of the dome.
• Then I bricked-up the opening to smother the fire and let the heat even out throughout the dome. The whole process took me about 1 hr. but I was fussing a lot, Tomorrow I will know more what to expect and should be able to do it quicker.

Some observations from day 1. Depending on how the wind is blowing, some smoke still comes out the front, I'm playing with arranging bricks at the opening to help the airflow inside the dome circulate and stratify, so the smoke is at the top 4" of the arch. We'll see how the airflow progresses as the dome and flue get steadily hotter.

The outside face of the top brick in the arch got to 100F. The stucco on the gallery is in good shape, still curing, since it has moisture on the inside face of the clear shrink-wrap covering, but that area never got hotter than ambient temps and neither did the perlcrete, which is looking nice and dry.

[UtahBeehiver]

Great curing start, be patient. This is where we see some builders say one more log won't hurt and it spikes the temp and causes cracking. If you see steam you are running too hot too fast. Look for condensation under the plastic which indicates mechanical water is still present in the oven.

PS where in Minneapolis, have a step son in White Bear

[Sixto]

UtahBeehiver (I responded to your P.S. via private message) Yes, I feel more confident about being able to control temperatures after today.... Starting with charcoal briquets was easy, and adding small pieces of kindling about 1" in diameter and 4" to 6" long seem to be a good way to build up slowly.

[david s]

Great result. Be careful and patient because now is the time builders get excited and hurry things along with damaging results. Almost there, don't sprint to the line.
Once the starts really drying out, the black soot will begin to burn off at the crown of the dome (this happens at around 300C) If you shoot a temp at the base of the dome you will find that it's barely 200C and it's this difference in temperatures ,which also mean difference in thermal expansion, That can be damaging. Slowly the white will extend down the dome, but there is often a persistent ring of black around the base of the dome. This is an indication of cooler temperature there, so instead of making the fire bigger try spreading it out so there's less flame impingement on the top of the dome, but more at the base. You're done when the whole dome has turned white.Then you are ready to add the outer render layer(s)

[Sixto]

Once the starts really drying out, the black soot will begin to burn off at the crown of the dome (this happens at around 300C) If you shoot a temp at the base of the dome you will find that it's barely 200C and it's this difference in temperatures ,which also mean difference in thermal expansion, That can be damaging. Slowly the white will extend down the dome, but there is often a persistent ring of black around the base of the dome. This is an indication of cooler temperature there, so instead of making the fire bigger try spreading it out so there's less flame impingement on the top of the dome, but more at the base. You're done when the whole dome has turned white.Then you are ready to add the outer render layer(s)

Perfect, thanks for adding all the detail above, I will go slow and keep an eye on the color of the dome interior.

[Sixto]

FIRE IN THE HOLE! (Day 2)

Took my time building up to temp, but it got a little hotter anyways - 316F, no harm done. Temp was down below 300F in a few minutes. The best news is that even without an insulated door (just bricking up the opening) the inside of the dome was 86f, while the ambient temperature was 52f this morning at around 8:00 a.m. (a day after the first fire to 200F)

The oven still smokes a bit out the front of the gallery vault, but less than yesterday.
The soot inside the dome is not clearing anywhere yet.
I need a shower to get the wood smoke smell out of my hair...

[UtahBeehiver]

New oven will smoke a lot until cured.

[Sixto]

Well, I wasn't trying to rush or anything, but I guess I went too far. Today's temp goal was 400F.
I started with charcoal briquets, was up to about 250f, so I added some sticks that were 6" long by 1" wide. (like Russell said - one stick too many can send it over the edge)
Then the temperature spiked from 300F to 600F in a matter of seconds.
I spread the coals around the dome to cool it down, and make the heat less concentrated - but as you can see below, a 1mm crack appeared at the top of the dome arch.
Not the end of the world, but disappointing after trying to be as cautious as I could.
Oh well.... I will wait till it cools down further and hope the crack doesnt go too far up on the inside of the dome....

I guess the lessons here are to add 1 stick at a time, wait 3-5 minutes, and if more heat is desired, add ONLY ONE more stick, and wait 3-5 mins each time.
Be ready at all times to spread the coals, especially as you start to approach Pizza Temps (400F and higher).
At these temps, I'd rather even out the heat throughout the dome, than to keep it concentrated in the middle.

[UtahBeehiver]

Every oven cracks somewhere. If a builder says their oven hasn't cracked then they should go into politics or sell use cars.

[MarkJerling]

Yup. there are two types of ovens: Those with cracks and those who's owners can't see the cracks. Don't sweat it Sixto

[Sixto]

Thanks Russell and MarkI believe you, but I wish I had of those "invisible cracks" that some ovens get...
I will get over my disappointment tomorrow, and build even slower, more distributed fires for the rest of the week.
Even though it got as high as 600F today, i will also stick to the schedule and try to stay close to 500f tomorrow.

[Sixto]

FIRES in the Hole! - Day 4 - goal is 500F

Today it was a much more controlled climb, I got just around 500F in about one hour, split the coals into two groups: left-rear and right-rear, and slowly added single pieces of kindling (1 at a time every 3-5 minutes).

A few observations: I tried to throttle down the arch opening with a few bricks, mostly to see if I could get the smoke out of my eyes - but noticed the fire got smokier when I did that (which I'm interpreting as less efficient burn, not enough oxygen to fully burn the secondary combustion gases) When I opened it up, the smoke cleared, the fire got visibly more active, and temperature climbed.

This time I also noticed the walls below the dome apex were about 50F cooler than the apex... (vs 100F to 150F cooler) and also the floor was warmer than yesterday. I think this is partly due to the distribution of fire into two areas vs one, and the additional amount of time the fire had to soak the dome bricks. Remember that yesterday my goal was 400F, but I accidentally got to 600F. Yesterday's fire was both quicker and more concentrated at the center.

Finally, I noticed the fire got a little bit hotter when all of the sticks became embers, something to think about when building up the temp... a flaming stick produces light and heat; a glowing ember gives off less light, but perhaps more heat? This time I'm letting the fire die down naturally instead of bricking up the archway.

The crack is still there, but bothers me less already. I don't know how far up the dome it goes... It was narrower when I started, then it opened back to 1mm while I got the oven up to temp. I'm starting to see it as a sign of the oven's character insted of my stupidity, sort of like Harry Potter's lightning-bolt scar. I guess we never know what we don't know until we try to do something! (even when we're repeatedly told what's likely to happen - heh, heh)

[Sixto]

FIRE IN THE HOLE DAY 6 - Goal is 600F


A bigger, hotter fire, started by spreading charcoal in 3 areas along the back of the dome, and adding sticks gradually until I reached 600F at the apex of the dome. This gave me a nice, even distribution, and an easier way to control the temperature climb. Still, it takes a while to soak the dome evenly (about 90 minutes fussing with the fire)...at the point the photo was taken, I had consolidated all the embers on the left side, and the apex of the dome, plus the entire right side of the dome was around 480F, and the floor was about 310F.

I'm not too concerned that some areas were hotter than 600, since I had already (accidentally and momentarily) reached this temperature 2 days ago. I was more concerned with minimizing the temperature variation across the entire dome, not having a huge hot-spot, and controlling the overall rate of climb.

There are NO areas where the soot is clearing out completely yet... I'm expecting to reach that tomorrow, at least in part of the dome, when I get to 700F. If you look carefully at the bottom edge of the dome arch, it's a little lighter than the top of the arch, but not much...

Every day I get more of a feel for how the oven works, so I think there is as much value in using the drying fires as a learning opportunity, as it is a way to gradually dry the dome bricks and perlcrete layer. The perlcrete got a little hotter all around - about 110f. Ambient temperature was around 70F.

[UtahBeehiver]

Gulf and I have notice that there is a unique smell as the carbon burns off and dome is clearing.