Brick oven reconstructed to a steel one

[david s]

Re: Brick oven reconstructed to a steel one

The 1/2" steel plate floor is quite a lot of thermal mass, probably around three times the total weight of your entire oven. He also has 2" insulating blanket where yours appears to only be partially covered by 1" of blanket. So you have way less heat storage and much less insulation. Keep experimenting.

[v12spirit]

Re: Brick oven reconstructed to a steel one

Adding some thermal mass to the hearth is simple and achievable by laying a "thicker" layer of bricks. But the hesitation is to or to not add thermal mass to the dome which requires some effort and more importantly will require me to bring another box of IFBs in order for the refractory layer to settle on a stable base contrary to my current case where I can compensate for the lack of IFBs by stuffing the gaps in between with ceramic blanket and the oven can still stand robust on that. That is the question. If I want to add some thermal mass to the dome, how can it be achieved without requiring one more box of IFBs, which is not cheap neither easy to bring one more again?
I have been educated in the forum that thermal mass must be thicker on the dome than on the hearth, but I still see ovens with just 16-14 gauge steel sheet dome and a thick layer of brick and steel on the hearth like acfbob's oven and the Forno's Bella oven and are running so fine. I'm a little bit confused.

[v12spirit]

Re: Brick oven reconstructed to a steel one

I laid a layer of 2" bricks on the hearth, 1.5 Kg dry wood, gave it a match. 25 minutes later, the oven's is hot but not enough to burn a bench of semolina on the floor in 3 seconds; it took 15+ seconds, but it burned. I strongly believe it is the insulation. I will insulate the oven tightly and see.

[v12spirit]

Re: Brick oven reconstructed to a steel one

Am thinking of installing a damper on the vent in order to trap some of the escaping heat from the chimney. For convenience, I prefer to install it in place of the yellow rectangle on the picture. Is that technically correct?

[felix]

Re: Brick oven reconstructed to a steel one

V12,

I am no expert in venting so take this advice for what it is worth, but I would be very cautious in restricting the exhaust gases if this were in my house. I would lean to build a door that would restrict the air getting to the fire instead. No need to risk any carbon monoxide buildup!

Carl

[kbartman]

Re: Brick oven reconstructed to a steel one

V12,

I am no expert in venting so take this advice for what it is worth, but I would be very cautious in restricting the exhaust gases if this were in my house. I would lean to build a door that would restrict the air getting to the fire instead. No need to risk any carbon monoxide buildup!

Carl

I second that motion. Nice metal work, watching with interest

[v12spirit]

Re: Brick oven reconstructed to a steel one

I insulated the oven more tightly. It performed far better. But a couple of things are tempting me to clad the dome with a heat reservoir


1st, the oven, when run for just a few pizzas and done, will be more fuel efficient without the reservoir. But considering running the oven for a feast, where the oven will run for 1-2 hours to bake the big amount of pizzas/pies, and considering the human delay where the 400 C oven is far faster than the pizza/pie maker to cope with (which is an unavoidable bottleneck) will result in the oven burning wood in elapsed time to keep hot since it has low thermal mass which is a waste of fuel that would be better reserved in a heat reservoir. Even the idea of running the oven for more than an hour makes it more fuel efficient with the thermal mass (heat reservoir) since it would be saturated after an hour (I will not add more than 1" cladding if any) and will need just a small fire to keep that heat. I did experience that in my experimental runs that I was doing to my oven.


2nd The dome recharges the hearth, and IMHO it is more efficient for the oven to make the dome have more thermal mass than the hearth.


3rd A lesson I learned from "open-door" ovens: The thermal mass compensates for heat loss through the opening.


4th the thermal mass resultant retained heat cooking is very tempting. Just adding the fire bricks to the hearth extended the cooling down of the oven while the door is opened to 8+ hours that allowed for slow cooking of meat/chicken, making jacket potatoes, or roasting almonds with no fire at all.
My belief is that my aim of fuel efficiency is NOT strictly achieved by the LOWEST thermal mass. My belief is that I need a thermal mass but I haven't done the math for how much thermal mass is optimum to satisfy all what I have mentioned above.
My goal is to make use of as much thermal energy released by the wood as possible.


Question: I have these options for cladding the oven:
1- Crushed basalt with cement
2- Homebrew (3:1:1:1) sand,clay, lime,cement.
3- Crushed bricks with cement and lime (without sand)
which is better in holding heat? and may I increase the lime ratio in option 2? I obviously have no structure issues for my cladding. It will just rest/lean on steel no matter how thick or how strong it is. It is there just to "thermal-mass" the oven.

[cobblerdave]

Re: Brick oven reconstructed to a steel one

G'day
Or one not mentioned
Basalt gravel, sand, Lime and Portland cement. Basically lime rich concrete.
Like concrete the sand fills in the spaces between the gravel, giving you a dense product. A small amount of Portland give the initial "set" . The larger amount of lime, the higher temp glue and so I think more resistance to cracking than the Portland.
I'm by no means the expert , but this is what I'd start with.
Regards dave

[david s]

Re: Brick oven reconstructed to a steel one

G'day
Or one not mentioned
Basalt gravel, sand, Lime and Portland cement. Basically lime rich concrete.
Like concrete the sand fills in the spaces between the gravel, giving you a dense product. A small amount of Portland give the initial "set" . The larger amount of lime, the higher temp glue and so I think more resistance to cracking than the Portland.
I'm by no means the expert , but this is what I'd start with.
Regards dave

I agree. Placing a thin layer of refractory mix directly against steel is likely to result in its failure as the more conductive stainless will want to expand before the refractory has time to heat. This will result in cracking of the layer. A gap between the stainless and the refractory to avoid this would be counterproductive as you want the conductivity so the heat will transfer. You are right in saying that strength in the refractory layer is hardly of consequence as it is merely mass and held in position by the stainless inner walls. If it were mine I'd be using lots of stainless steel needle reinforcing though and making the layer closer to 2" than 1"

[v12spirit]

Re: Brick oven reconstructed to a steel one

Thanks mates for your continuous advising. The crushed basalt available to me is as fine as sand. The refractory layer will be divided into 4 separate masses each is the size of the four steel pieces constituting the dome (the flat dome and the three pieces of the side wall). These three masses of the refractory layer are separated by 3 cm steel belt running all over the welds connecting the four pieces and perpendicular to them. This lessens the opportunity of cracking, and guarantees the refractory pieces are constrained in place regardless of any possible individual expansions between the steel and them.
I will use the formula suggested by dave, but why did not it include clay? and what the ratios you recommend best? Moreover. I have two kinds of sand, one is yellowish white, and the other is red. What is the prefered among these?

[cobblerdave]

Re: Brick oven reconstructed to a steel one

G'day
The clay is only included in the homebrew mix to make it more plastic and workable in its "wet" state. . Once cured it has no other function. In fact if too much is included it will probably lead to cracking as it dries rather than being fired.
Davids could explain this better than me.
Regards dave

[david s]

Re: Brick oven reconstructed to a steel one

G'day
The clay is only included in the homebrew mix to make it more plastic and workable in its "wet" state. . Once cured it has no other function. In fact if too much is included it will probably lead to cracking as it dries rather than being fired.

Regards dave

Yes, you are quite correct. Clay is made from decomposed rock and its particles are extremely fine, so in effect it is simply a superfine aggregate. The temperatures we fire to are insufficient to sinter the clay ie. make it permanent. The problem with the extremely small particle size is that it shrinks more on drying as the particles cling to each other. This shrinkage can create cracks if a high proportion of clay (over 20% or so) is used.

[stonecutter]

Re: Brick oven reconstructed to a steel one

G'day
The clay is only included in the homebrew mix to make it more plastic and workable in its "wet" state. . Once cured it has no other function. In fact if too much is included it will probably lead to cracking as it dries rather than being fired.

Just to clarify, addition of fireclay to the 'homebrew' mix makes it a fire resistant mortar...lime is more of the plastisizer/cementitious component. Without clay, you will have a mortar that has very poor resistance to thermal cycling. As far as cracking, it's going to happen, clay or not. Reinforcement is a critical component to this kind of application ( masonry mass over steel ) as david mentioned.

[v12spirit]

Re: Brick oven reconstructed to a steel one

Thank you all for the helpful inputs. Could you give me the formula with ratios to start with? I don't want to be improvising on my own. One more question. Does the fine crushed basalt work? or should I look for coarse basalt I mean to lessen cracking?

[david s]

Re: Brick oven reconstructed to a steel one

Thank you all for the helpful inputs. Could you give me the formula with ratios to start with? I don't want to be improvising on my own. One more question. Does the fine crushed basalt work? or should I look for coarse basalt I mean to lessen cracking?

Making your own castable is improvising. That is why I use a proprietary castable. You may have success with your own brew, but it may also fail. The home-brew 3:1:1:1 sand, cement, clay and lime works well for our application. I don't know how well the basalt works, but the advantage of it is that it usually contains a variety of grain size which is a desirable quality, we call it cracker dust here and it's very cheap because it's the leftover material after the larger aggregate has been removed.