Another Minneapolis WFO

[david s]

If you drive out all the moisture from the vermicrete layer before rendering over it, some of the moisture from the outer render will be sucked back into the vermicrete. To reduce this loss I simply wrap the whole oven in cling wrap once the render has been applied, then leave it for a week. Little beads of moisture are visible under the cling wrap indicating that the moisture is being held in.

[UtahBeehiver]

IMHO, you could start slow curing of the oven after you install the ceramic fiber insulation. Have you considered install a vent at the apex of the dome during the p/vcrete stage? No matter what you do water has a way of sneaking in and when it sublimates from liquid to vapor the volume increase by a factor of 1500 times and can build up pressure under the dome enough to crack stucco. A vent allows water vapor to egress out. Cheap insurance and can be done around $10. Plenty of examples on blog.

[Sixto]

IMHO, you could start slow curing of the oven after you install the ceramic fiber insulation. Have you considered install a vent at the apex of the dome during the p/vcrete stage?
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Thank you both, and yes, I am planning to have a vent at the top of the dome to relieve any vapor pressure. I was thinking that it would be best to not have any drying fires during the perl-Crete installation, just to allow that to set for 5 days before starting the drying fires, I figured one weeks wait is not much in the scope of the project.

[Sixto]

Arch form removed, interior tuckpointed, and first layer of chimney bricks cut - there are 12 total, but these center 8 are being mortared in-pairs and dried in plastic bags to get a nice strong joint, and make it easier to install since the shorter 4 bricks in the center tended to tip-into the flue cavity.

Taking a break for a few days to smell the roses.

Pretty deep gallery... to be covered by 1" thick fiber reinforced stucco. (no insulation over the gallery or flue, just over the dome)


Hopefully big enough (18-1/2"d x 36" wide x 22" tall at center) to give me easy reach into the oven, and also grill on non-oven days.
every other course of the vault proper (yellow bricks) is done with used #2 arch bricks sourced from a dismantled wood kiln at the U of M. (Dome arch is all #2 arch bricks)


First layer of chimney bricks cut - gradual transition from 8" x 12" arch opening to 6" dia. stainless flue.

[david s]

The larger the arch radius the greater is the sideways thrust. I’d be concerned about the structural integrity of the arch and be inclined to parge it with a one inch layer of cement render reinforced with chicken wire or fibres. Although I am really not sure if this is necessary. Ask some of your architectural colleagues what they think.

[Sixto]

I will be adding 1" fiber-reinforced plaster/render layer on top of the flue gallery brick as you mentioned. (Thank you) That's what I love about this forum, Ideas can be tested, and either proven right or wrong. if the arch cracks even after the reinforcement, then we'll know that wasn't enough - and then - I would rebuild it with another layer of staggered-joint bricks instead. We'll find out one way or another.

99% of Architects wouldn't know how to calculate the answer, (I can say that 'cause I have a Master's degree in Architecture and used to be a Licensed Architect before I retired ) A Structural Engineer would know how, charge me real money to run the calculations, and then would probably flip a coin in the end, because of the untested homebrew mortar, uncontrolled site conditions, and unskilled labor. So a reinforced plaster/render layer may not be necessary, but I'd rather be safe than sorry. I've put way too much effort into this oven already, and my bricklaying skills are so remedial, that some degree of "belts and suspenders" seems like a wise investment.

My artist wife says a thicker arch might look better, and we're covering the whole thing with tile next year anyway! (then I get to make the front arch-edge pretty again)

Adding back view of the gallery to show where the flue gallery meets the dome, the gallery is actually 9" thick there (see post #81) but the main purpose of that is to minimize the gap between the flue-gallery and dome-arch when looking at the oven from the front. (about 1/4" gap filled with compressed 3/4" braided high-temp rope sealing the gap in front, and 1/2" ceramic fiber blanket backup, to provide a heat-stop between the dome and the flue gallery.)

[NCMan]

Just wanted to jump in and say again how impressed I am w/your work. Good job!!

[Sixto]

Thanks NCman! I enjoyed browsing your build thread. Sixto

[Sixto]

Insulating the dome.... for a 36" diameter dome I purchased two rolls of 1"x 2'-0" x 25'-0" and that was enough for almost 4 full layers (the top half got one extra layer of blanket), so I am thinking of mixing the perlite a little stiffer, maybe 8:1 perlite to cement ratio by volume, and going a little thinner, maybe 1" instead of 2". The thought being this: Since I have more blanket insulation than I thought I would, the perlite layer main purpose now is to give the stucco a stiffer and rounder substrate, and provide a breathable space for the vent on top of the dome.

The fiber insulation was definitely a hot and sweaty 2-person job, my son came over to help and we had it done under 2 hrs. Fully masked, eye protection, rubber gloves, long sleeves and pants that went into the laundry immediately all by themselves. Each layer tucked-in nicely into the back of the flue gallery, and the top layer is tied down with galvanized wire, all of it was covered-up with plastic until the perlite arrives.

Now, the 12 chimney bricks were another story... I tried to mortar the 4 pairs plus the 4 singles yesterday, and had a frustrating time trying to align it all without messing up the fresh mortar joints, so I took them all down and tomorrow I will mortart more bricks together so I end up with 4 sets of 3 bricks each, Then when those are set together, I will mortar the two sets in the the back half first, make sure that is solid and square, and then add the two front sets of 3 bricks each so I only have to mortar and level 2 sets at one time.

I also tried doing the stucco along the outside of the flue gallery, and realized that doing the stucco and mesh while also trying to mortar the chimney bricks was just too much to tackle. The mesh is rather tight 1/8" alkali resistant mesh typically used for concrete counters, and the manufacturer recommends using two layers when going thicker than 1" (a 75' roll was about 1/2 the price of A/R fiberglass lath) so I will mix the stucco in 2 or 3 batches, and lay the mesh in two steps to make sure it is fully embedded in the stucco, and the stucco is fully adhered to the wet bricks of the gallery. I also want to use this on the stucco/render over the perlite layer of the dome. If there is enough mesh left after that, I may even skim-coat a 3rd layer of mesh on the very top of the gallery stucco.

[Mr. Slowhand]

99% of Architects wouldn't know how to calculate the answer, (I can say that 'cause I have a Master's degree in Architecture and used to be a Licensed Architect before I retired ) A Structural Engineer would know how, charge me real money to run the calculations, and then would probably flip a coin in the end, because of the untested homebrew mortar, uncontrolled site conditions, and unskilled labor.

This sentence is why I love FB forum. Don't sell yourself short on the unskilled labor Sixto!, It is looking good until now!!

[Mr. Slowhand]

Just a question, are you covering the entry gallery with the blanket also, or just doing the perlite?

[Sixto]

Just a question, are you covering the entry gallery with the blanket also, or just doing the perlite?

I'm not insulating the gallery (only the dome) for the following reasons:

a) I have no desire to retain heat in the gallery, since it's wide open and will only be used for grilling and accessing the oven. I am working on an insulated door design that will cover the exposed front face of the dome arch bricks, though.
b) Where the gallery comes closest to the dome (around the 3" deep dome arch projection) it is isolated from the dome by insulating rope and 1/2" thick ceramic blanket
c) The size of my flue gallery is relatively larger than others I've seen, so I'm hoping the smoke will go straight up into the collector funnel and flue, mixing with the ambient air and cooling down as it goes up. (I may end up with a permanently sooty gallery interior surface but it remains to be seen)

i am planning to add 1" of fiber-reinforced stucco and terra-cotta tiles to the outside of the dome and gallery, hoping to add some strength and weather protection to the 4.5" thick brick gallery vault.

[AJH]

Hey Sixto, been watching your build while planning mine. I was thinking that adding a lip on the inside of your gallery might trap the smoke in there and force it to the chimney. I'm not sure if you want to reduce the opening though, but it might help with smoke control and keep the front from getting sooty. Maybe just one arch of bricks inside the main arch?

-AJ

[Sixto]

Thanks AJ! I thought about having a lip, but like you said, I chose to maximize the interior height. Instead, to encourage the smoke to stay near the flue, I tilted the vault form down 1/2" at the front (only noticeable with a level) and beveled the bottom-rear corner of the bricks in front of the flue opening by 2". I'm hoping this will pull-in fresh air along the top of the gallery into the flue funnel and keep the smoke close to the back.



We'll find out soon enough, I'm impatient to start drying fires, now that the dome is covered with 4" of ceramic fiber blanket, I can't get perlite this week, so I'm falling behind my schedule. I'm also waiting for my flue bricks to set in their groups of 3 bricks before I can mortar them in, perhaps this weekend???

[mongota]

Just catching up on this...your build looks terrific!

I did the same thing with my chimney anchor bricks, I made a rectangular wood frame and mortared the bricks up in two groups of six within the form. The next day I mortared the two sets on top of the arch with the wood frame holding them secure. It worked very well, saving a lot of "tap tap tap stay put!" frustration.
https://community.fornobravo.com/for...481#post406481