Mongo's 42" CT Build

[Lburou]

You have made a remarkable oven, well done!

My take on oven moisture: If it is fired once or twice a week, the oven heats more quickly, gets hotter, and stays hotter longer than when Moisture builds up from disuse.

Firing the oven, even to an intermediate temperature goes a long way to controlling moisture. You can't get rid of a lot of moisture with just one firing cycle though. The solution is to use it more often. ;-)

Keep in mind that wood contains at least 8-10% moisture, sometimes a lot more. This moisture makes a more moist heat than in your kitchen's oven. There are pluses to baking with that moisture given off by the firewood. JMO

[mongota]

Vent Cap update...

I was a bit skeptical regarding the need for a vent at the apex of my dome, but for a couple dollars in materials and 15 minutes of my time I incorporated one. Why not?

I used black pipe with a threaded cap.

After a few months of sitting dormant, Ifired up the oven yesterday and a couple hours in to the firing, I thought "why not?". So i climbed up and unthreaded the cap. Moisture!

The inside of both the cap and pipe were wet.

I left the cap off and when i put it to bed for the night i reinstalled the cap. Came out today and popped the cap off. More moisture


I have 4" of CF board insulation under the floor. I have 4" of insulation over the dome (four 1" layers of CF blanket).


So, I'm sold. It certainly does seem to be a valid escape path for moisture within the dome structure.

[mongota]

Love your work Mongo! Great stuff!

I appreciate those words Mark. Thanks you.

[MarkJerling]

No progress, just an update, I just don't think I ever posted any overall shots of the oven with the stone work done. Here are a couple; front and back.

Love your work Mongo! Great stuff!

[Baza]

Keep the dream alive Mongo ... keep the dream alive!

[mongota]

AH HA!!!

First - if there is one thing you cannot be accused of it's lack of clarity - I mean ... who else takes the time to use one's own pics/drawings to help teach them!?
AWESOME! There is a natural teacher in you!

Second - this makes total sense (though my math was off in my original drawing!).
Yes - I get it now -

Given I would like to follow a similar approach (and apply it to a flared opening - if, that is, flared doesn't mean more cold air to deal with), it still allows the remnants of a cut 9" brick (into 6 1/8" and 2 7/8") to serve as material for the outer arch brick assembly (given your build's 2 3/4" thickness on the outside brick arch). It's the Scot in me that doesnae want to waste!

Wonderful Mongo ... I will take all this learning into the weekend with me!
Fingers crossed!
Barry

I knew I was creating waste...but until my wife didn't want it any more (at least it's on a back-back-back burner), I was going to use the offcuts to build a tandoor oven.

[Baza]

AH HA!!!

First - if there is one thing you cannot be accused of it's lack of clarity - I mean ... who else takes the time to use one's own pics/drawings to help teach them!?
AWESOME! There is a natural teacher in you!

Second - this makes total sense (though my math was off in my original drawing!).
Yes - I get it now -

Given I would like to follow a similar approach (and apply it to a flared opening - if, that is, flared doesn't mean more cold air to deal with), it still allows the remnants of a cut 9" brick (into 6 1/8" and 2 7/8") to serve as material for the outer arch brick assembly (given your build's 2 3/4" thickness on the outside brick arch). It's the Scot in me that doesnae want to waste!

Wonderful Mongo ... I will take all this learning into the weekend with me!
Fingers crossed!
Barry

[mongota]

Mongo - you, again, provide this Forum so much clarity and support - thank you for doing this!!
I am certainly a builder that is wondering the very things you posted!

I am sharing a photo I drew quickly (at work in my office - tell NO ONE!) of your vent build with a question....
You indicated your vent landing is 13.5" ... the length of a full and half brick.
You indicated that you overlapped your oven arch opening by 1.625" to cover the rope heat break

Doesn't the lip of 1 5/8" subtract from the overall length of a full and half brick (13.5") to make it actually 11 7/8" from oven opening to vent opening?
Don't you lose length on the lip at the dome arch?

Sorry to be detail-y ... your build has helped inform mine SO much ... my brain just needs to stop hurting over this!

Thanks Mongo!
Barry

Your welcome Barry Baza , thanks for the kind words.

Regarding your question, I must have explained it poorly in a previous post, but it's the exact opposite. That roughly 1-5/8" lip is added to the 13-1/2" length. So the INSIDE length of my tunnel is exactly 1-1/2 bricks, or 13-1/2" long. The OUTSIDE length of my tunnel is 13-1/2" PLUS the 1-5/8" extension from the "L", or about 15-1/8".

[Baza]

Mongo - you, again, provide this Forum so much clarity and support - thank you for doing this!!
I am certainly a builder that is wondering the very things you posted!

I am sharing a photo I drew quickly (at work in my office - tell NO ONE!) of your vent build with a question....
You indicated your vent landing is 13.5" ... the length of a full and half brick.
You indicated that you overlapped your oven arch opening by 1.625" to cover the rope heat break

Doesn't the lip of 1 5/8" subtract from the overall length of a full and half brick (13.5") to make it actually 11 7/8" from oven opening to vent opening?
Don't you lose length on the lip at the dome arch?

Sorry to be detail-y ... your build has helped inform mine SO much ... my brain just needs to stop hurting over this!

Thanks Mongo!
Barry

[mongota]

Chimney draw update.

I've had an untold number of fires in this oven, but a question posted by another builder CapePizza gave me reason to take a couple of photos when I lit a fire last night. The concern was how much smoke escaped out the front of the oven when a fire was started.

A couple of quick points...the moisture of your wood will have an effect. Moist, wet, damp, unseasoned wood will smolder and take longer to develop than dry seasoned wood. With the fire taking longer to establish, getting a good draw up the chimney may be delayed, resulting in smoke wafting out the front of the oven. Second is "the size" of it all. The size of the chimney throat. The size of the ID of the chimney. The size of the height of the chimney.

My oven is 42" in diameter and has an 8" ID double walled and insulated chimney pipe. The brick throat is an 8" square, but the bottom of the throat that you can see from the landing is flared out, so the bottom is about 10" square. In the end, the fire sees a 10" square opening that transitions to an 8" square opening that then transitions to an 8" round chimney pipe. As far as square inches of opening, the flared part of the throat is 100 sqin, then it goes to 64sqin, then to the chimney pipe of 50sqin. My current chimney pipe is 4' tall.

When I lit the fire last night, I built it right at the opening. A couple of the smaller branches even extended out of the opening by an inch or two. The wood was ambient moisture, stored outside, oak, split by me earlier this year. Maybe seasoned 5 months. There were also a couple of branches, 1-2" in diameter. One piece had more moisture than typical, with moisture bubbling out of the end grain as the fire burned.

I have to say I was surprised by the fire. I'd have to say almost no smoke escaped out the front of the oven, even at the initial lighting. Just an occasional wisp. I did not prime the chimney draw with a burning piece of paper held up in the throat. Most notable, or telling, is how clean and soot free the face of the brick arch is , as well as how clean the underside and face of the decorative cast concrete arch is. Zero soot, even after so, so many fires. The BOTTOM of the brick arch? Soot. It burns off, but it shows some smoke is hitting the brick. But no soot on the front of the arch brick, and no soot on the bottom of front of the cast concrete arch? That makes me happy.

My landing tunnel is 13-1/2" deep. With the throat opening being 8" square, that leaves 5-1/2" divided by 2, or about 2-3/4" of brick in front of and behind the throat opening. With a roughly 1" flare, the bricks actually have about 1-3/4" at the bottom of the throat, the top of the throat has the full 2-3/4".

It performs well. Hope this helps!

[Dr.Lee]

Thanks very much for the detail.

[mongota]

Lee, I tried adding a photo to the previous post but could not. Here's a shot from below...the 8" round from the anchor plate in the ~8-1/2" square throat. The 8-1/2" is a bit of an estimation, I just wanted the throat opening to be slightly larger than the anchor plate round to maintain a little lateral play for locating the actual chimney dead-center on the arch.

[mongota]

Can you tell me the approximate dimensions of the throat on your vent arch? I've been looking at the photos of the throat on page 6 of the build and counting bricks but I am unsure about the length of the partial bricks I see. Thanks - Lee

I used an 8" ID chimney pipe. The chimney anchor plate I used has an ~8" round running vertically through the horizontal anchor plate. The portion of the round that extends below the plate sits inside the square opening of the throat. I made the throat slightly larger than the round, so the opening in the throat itself is maybe 8-1/2" square.

[Dr.Lee]

Can you tell me the approximate dimensions of the throat on your vent arch? I've been looking at the photos of the throat on page 6 of the build and counting bricks but I am unsure about the length of the partial bricks I see. Thanks - Lee

[mongota]

Thanks! I need to get my door pics posted.