Another Minneapolis WFO

[Sixto]

Photo Update: Last week was spent cutting the tops of the soldier course, and the many small pieces to finish the herring-bone floor pattern as tight to the cardboard shim as I could make it.

Today my buddy Nick and i mortared-in the soldier course and I started cutting bricks for the dome-arch. I was able to source a number of used #2 arch brick which fit my form much better and will save me time with the arch and gallery.

Cutting bricks is not as hard as I thought it would be, I've yet to completely ruin a brick.... (I may have had to whittle it many times, but it got used in the end). Part of the difficulty is that since it is relatively easy to cut them, I am trying to be that much more precise in my layout, trying to avoid stacking vertical joints.

Mixing the homebrew mortar was also relatively easy... I used a 35-oz Fage yogurt container to measure (we eat a lot of yogurt): (3) sand, (1) cement, (1) Hydrated Lime and (1) Fireclay dust. The first batch of mortar stayed workable for about an hour and allowed us to set most of the soldier course. Another half-batch was needed to finish.

Tomorrow, I will cut and mortar the first chain above the soldier course.

Sixto- Minneapolis.

[MarkJerling]

The Searching for Sugarman doco was great.
I think you'll be happy with the change to herringbone. Make sure you have it set so that you have the floor joins angled to the entry. I did my floor to a template, which I moved around until I had the least "slivers" but there's always some funny little pieces.

[Sixto]

Looking good.
Completely unrelated, but every time I see your name I am reminded of one of my favourite music artists, Sixto Rodriguez.

Thanks Mark! - I don't come across many people that are familiar with my name.... most of the time I get "Huh?" but it has served me well. I also like Mr. Rodriguez's music, and also enjoyed seeing the movie about his comeback, titled "Searching for Sugarman".

Today I'm cutting bricks for the first course above the soldier course, and getting all confused with angles....
will post more progress photos once I have it sorted out, I hope I don't ruin too many bricks in the learning process.

Also, even though the photo on post 38 shows it differently, I changed my mind for the fourth or fifth time (after weighing the potential increase in heating time) and laid the floor bricks in a herringbone pattern with the 4.5" dimension vertical. Leveling was easy, but I'm also having a heck of a time cutting some of the small brick wedges that meet the soldier course (with an 18" gap) The herringbone pattern is not so easy to fit into a 36-sided polygon.

Here is how I set up the saw jig for the tops of the soldier course...that was easy!

Sixto.- Minneapolis.

[MarkJerling]

Looking good.
Completely unrelated, but every time I see your name I am reminded of one of my favourite music artists, Sixto Rodriguez.

[Sixto]

Progress Photo.

The brick jig is working fine, I did place the hinge on the far left, and allowed space for the cutoff piece. So far I have not had to do compound angles, but the first few cuts were a breeze. Next I will cut the tops of the soldier course to the angle made by the IT. Then I will mix and apply the homebrew mortar with 3 parts sand, I part Portland Cement, 1 part Hydrated Lime and 1 part Fire Clay powder. We'll see how that goes.

Six.

[Sixto]

...build the arch, then place the fiber tape against it, then build the flue gallery tight against it...

Makes sense - I've been thinking about the heat-break as if it were sealing the gap between a wood stove or oven door and the main body, but in fact, there is no opening/closing like a door, thus the gap only needs to be large enough for whatever material the heat-brake is made of. A thinner rope material still feels right to me for sealing-off the side facing the fire because of less chance of fibers fraying or falling on the pizza, but I like the idea of fiber behind it to seal the majority of the gap and promote a consistent spacing between the arch and the gallery. I also see the reason for an adhesive for holding the fiber in place when building the gallery arch tight against the dome arch. Thanks for the photo and clarification NCMan!

Here is a new question. I'm getting ready to cut bricks, and the saw-jigs I've seen at thread called "New idea for brick cutting table" (link below): all have the brick sloping down towards the saw blade. I built mine reversing the location of the hinge so that surface where the brick sits - is sloped up towards the blade (my saw has adjustable blade height). My thinking is to let gravity hold the brick in place away from the blade - via pivoting and locked-in place L-bracket, reducing the risk of the brick sliding towards or placing any pressure on the blade as the carriage moves forward during the cutting process...Photo attached.... Does anyone see a potential issue with this configuration? Having re-read the thread, I'm now also hinking of how to support the off-cut.

Referenced thread: https://community.fornobravo.com/for...-table?t=16780

Sixto - Minneapolis.

[NCMan]

Just a suggestion, but what I do is build the arch, then place the fiber tape against it, then build the flue gallery tight against it, instead of leaving a big gap and trying to stuff it shut. Also, a half inch is quite a large gap.

[Sixto]

Sounds good NCMan, thanks! - my plan now is to leave a 1/2" gap, stuff it with the woven fiber rope, and see how it holds, if needed, I will add a sealant, since that seems to be the standard practice in the forum.

Progress photos, slab is still curing in the form, but I removed the blanket after a week and started to lay out the base of the dome and flue gallery. Porcelain tile was the right price (60c / s.f.) so I cracked a few to get more channels to the 4 vents in the slab.

I also got about 70 broken insulating bricks for free along with my firebrick, so I'm doing two layers of insulating firebrick under the oven floor. (I just purchased new insulating firebrick for the 2nd layer)

Next, I'll work on my brick cutting jig and start shaping the rounded pieces at the base.

[NCMan]

I have used ceramic fiber tape on my heatbreaks, installed during the build. I personally would be more concerned w/some fibers from that fraying off and getting in food and/or lungs than I would some high temp sealant coming loose. There are many foodsafe high temp sealants out there. It can and will get pretty hot right there at the arch, as flames can lick right up there at that location. I would try to find something that can withstand those temps.

[Sixto]

You may come up with a more sophisticated design, but I’ve not found the need for anything but clever door placement. Share your results if you proceed with your idea.
Dave

Thanks again! - I am letting the thought simmer for a while before I make a decision, but I am leaning towards your approach.

I'm just full of questions today. Looking at High-Temp sealants for the heat-break. So far I've not found one that is labeled food-safe, even Rutland's 500d silicone sealant. There are several higher-temp options available also - up to 2000d. I'm weighing the potential toxicity of the sealant against the rated temp range, but can't find anything that 1) is safe and 2) can withstand the temperatures between the inner arch and the throat bricks (I'm guessing about 500d)

I also know the heat-break sealant would typically never come in contact with food under most conditions, (I guess some of it it could break off and fall on a pizza but that's unlikely) I just wonder if there is any downside to avoiding sealant altogether, and relying on a relatively tight friction fit by stuffing a woven high-temp rope into a gap from the inside of the arch. I suspect there may be movement in the arches when the oven is fired hot, and then there is chance that the rope sealing the arch may become loose if not adhered to the brick. I guess if that happens I could always buy a thicker rope? I kind of like the idea of having access to it from the inside of the oven throat , for future repairs and replacement...

Sixto - Minneapolis.

[david s]

In my oven if I place the door against the rebate it starves the fire of oxygen and the coals remain unburnt. Alternatively the door can be opened 1/2 to 1 “ which chokes the oven sufficiently to stop flame but still allows the coals to continue burning.
For smoking, which requires a low oven temperature like 120C I use a coffee tin with holes punched in the sides, filled with a few burning coals and a handful of smoking chips thrown in on top. With the door in place, but open a little to allow some combustion, it works remarkably well.
I also regularly roast meats, firing the oven for exactly one hour brings the temperature up to around 250C. I then push aside the coals place the broasting pan in the oven and throw 1/2 a handful of smoking chips onto the coals, then immediately place the door tight against the rebate. With the roast on a rack and half a cup of wine/half a cup of water in the roasting pan, it takes the sting out of the over hot floor and leaves the perfect amount of fluid in the roasting pan for making the beautiful Smokey flavoured gravy.
You may come up with a more sophisticated design, but I’ve not found the need for anything but clever door placement. Share your results if you proceed with your idea.
Dave

[Sixto]

Hi David, thanks for responding! - I will follow your recommendation on #1, and have a follow-up on #2 - Sixto.

2. The air inlet for the oven is provided by the oven mouth. A well designed flue gallery leading to a flue or chimney with an adequate cross sectional area is important.

I agree also with your note about question # 2 under typical WFO operations. I'm was thinking about two potential situations:
A) Using the oven as a smoker, or
B) Keeping a throttled-down fire overnight to save time and effort to reach a specific temperature in the morning (above and beyond the natural cooling of the dome) I was thinkiing of keeping a couple of logs in the dome overnight.at a slow burn rate, (just enough oxygen moving through to keep combustion going) with an insulated door in place to keep in most of the heat that's accumulated during the day, but let some (dampered) smoke escape either through the upper edges of the insulated door or a more controlled "window" cut into it.... The side combustion inlet would be closed off when the oven mouth is open and I'm tending the fire again...
(B) is something similar to what I currently do for my sealed-insulated fireplace, that is to choke down the air intake and the damper to promote a slow burn overnight... most of the wood burns while I sleep, keeping the firebox warm when I check it in the morning.)

I also wonder if I'm overthinking it. For example: if the oven is at 200d to 350d in the morning and I need 500d it may be easy enough to light it up again in the morning to build temperature relatively quickly.

[david s]

1. Keep it wet for a week. The strength build up is greatest as soon as the reaction begins, then slows down. Most of the potential strength gain has occurred after one week. Concrete strength tests are usually done after 28 days, but a week is considered sufficient. Best to throw some sheet plastic over the wet blanket to seal in the moisture.
2. The air inlet for the oven is provided by the oven mouth. A well designed flue gallery leading to a flue or chimney with an adequate cross sectional area is important.

[Sixto]

While I'm waiting for the slab to cure I had a few questions:
1). How long do I keep the curing slab covered with a wet blanket? It's been one day so far, and the top surface is already hard to the touch.
2) is there a case to be made for adding a closeable combustion air inlet at the base of the dome, and a corresponding closeable vent at the top of the insulated door? I'm thinking about maintaining temperature by re-stoking firewood overnight on day 2,3 or 4 to keep the oven temperature in a baking or roasting range...
thanks! Sixto.

[NCMan]

Happy to see you're back at it and looking forward to your build.