Brick oven reconstructed to a steel one

[v12spirit]

Re: Brick oven reconstructed to a steel one

Prepared the hearth; IFBs with ceramic blanket stuffed in between. Then returned the oven to its correct position with the help of the green line I drew all around the oven (Can be seen in the first picture), the oven settled neatly and firmly in place.

Next job, cladding....

[wotavidone]

Re: Brick oven reconstructed to a steel one

You got a point there. It is due to too many delay factors; life here isn't like it was before anymore.. It is hard for someone who didn't experience that to understand what I mean, I hope nobody would. That is all apart from the fact that the oven is experimental in hope to reduce heating up time without scarifying the good cooking properties of Pompei ovens.
Nevertheless, you are right at bothering the lengthy project period. The wife, dad, mom, cousins, and some friends do. I started feeling like an annoying dawdler, but I reserve the fact that I am knowing things they don't know; they just know that this oven should run fine, but do not know how this is achieved. Without my time consuming trials and errors myself would never have known all of that.

I apologise, mate. My comment was meant to be tongue-in-cheek, but a simple glance at the Wikipedia map captioned "current miltary situation" shows that there are currently 5 different groups laying claim to parts of Syria - and about half of the area shown is under control of ISIS. What a wonderful bunch they are. I do not know how you manage to survive in such an environment. I hope all goes well for you.

[v12spirit]

Re: Brick oven reconstructed to a steel one

I apologise, mate. My comment was meant to be tongue-in-cheek, but a simple glance at the Wikipedia map captioned "current miltary situation" shows that there are currently 5 different groups laying claim to parts of Syria - and about half of the area shown is under control of ISIS. What a wonderful bunch they are. I do not know how you manage to survive in such an environment. I hope all goes well for you.

No need to appolgies mate! I had got it and enjoyed your post. I even showed your post to my wife and by coincidence we were in argument about the finishing of the oven a few hours before reading it... We laught for long, and she said that she was right at her bothering and that you were the best member on the forum..

I follow a simple rule to survive; not to go out without necessity, not to participate in any group in any kind of participation, and to stick to my own life; enjoy what I can as much as I can, and forget about the war. Even this is not guaranteed for survival.

What is happening in my country is all wrong, and not guaranteed to lead to a definite end. Even those who claim to fight for religion are spoiling the whole religion, those who claim to fight for the country have destroyed the country, and those who claim to fight to protect civilians were the cause of killing thousands of civilians. It is a game of ego, nothing more. It says from the map!

Thanks for your kind wishes. I'm fine with the family so far.

[v12spirit]

Re: Brick oven reconstructed to a steel one

I decided to clad the sidewalls of the oven with the 3:1:1:1 formula, added to it a little bit of cheap wool threads 0.5-1 cm. I made an experimental mix and waited it until it dried out. It was weak actually. It could even crumble by hand. Is there anything wrong with the mix? or is that the inherent structure of it?
I am thinking of increasing cement and minimizing sand which I think is the cause of the weakness of the mix.
I am thinking of 2:1.5:1.5:1 - cement:lime:clay:sand. What do you suggest mates?

[david s]

Re: Brick oven reconstructed to a steel one

How long did you wait before crushing it? The lime in the brew retards its setting time. You may have not given it long enough. Try a week.
What is the wool for? They may impart a little strength but won't help in providing a network of pipes to allow water to escape because wool is actually pretty fire resistant.

[Tscarborough]

Re: Brick oven reconstructed to a steel one

"I am thinking of increasing cement and minimizing sand which I think is the cause of the weakness of the mix.
I am thinking of 2:1.5:1.5:1 - cement:lime:clay:sand. What do you suggest mates?"

That is exactly bass-ackwards. 3:1:1:1 is already too rich, it should be 6:1:1:1.

[v12spirit]

Re: Brick oven reconstructed to a steel one

Thanks mates for your inputs.

How long did you wait before crushing it? The lime in the brew retards its setting time. You may have not given it long enough. Try a week.
What is the wool for? They may impart a little strength but won't help in providing a network of pipes to allow water to escape because wool is actually pretty fire resistant.

I let it dry out for 3 days actually. Not long enough apparently.
Cheep (not cheap) wool was for moisture to escape. So with or without the wool is better since it gives some strength, and how long the threads should be and how much of it? For the moisture escape, what can I use?

[david s]

Re: Brick oven reconstructed to a steel one

Something is wrong in your brew. It should be hard in three days. Perhaps your cement was old and lumpy.
Wool fibres tend to cling to one another and fail to disperse evenly throughout the mix. The fibres you need are something that will melt at very low temperatures like polyproelene fibres, thinner than human hair (melting point 160 C) for every 10 L of homebrew mix add around 50 ml of fibres. If you can't get the fibres just take your time eliminating the water from the set mix.
If you want to increase strength, use stainless steel fibres (also called needles). Apart from increasing strength these increase the conductivity of the mix. Add a minimum of 2-3 % by weight.

[v12spirit]

Re: Brick oven reconstructed to a steel one

Something is wrong in your brew. It should be hard in three days. Perhaps your cement was old and lumpy.
Wool fibres tend to cling to one another and fail to disperse evenly throughout the mix. The fibres you need are something that will melt at very low temperatures like polyproelene fibres, thinner than human hair (melting point 160 C) for every 10 L of homebrew mix add around 50 ml of fibres. If you can't get the fibres just take your time eliminating the water from the set mix.
If you want to increase strength, use stainless steel fibres (also called needles). Apart from increasing strength these increase the conductivity of the mix. Add a minimum of 2-3 % by weight.

Thanks for the details david. The cement is fresh actually. When I used it with sand for other applications it hardened pretty well. May the reason be the ratio of the water? How much should it be?
Moreover. I see masons assuring to "water" any cement works for the first 3-7 days according to weather. They say that this helps it harden. I did not "water" my homebrew because I want moisture to escape. May that be another reason?

[david s]

Re: Brick oven reconstructed to a steel one

I decided to clad the sidewalls of the oven with the 3:1:1:1 formula, added to it a little bit of cheap wool threads 0.5-1 cm. I made an experimental mix and waited it until it dried out. It was weak actually. It could even crumble by hand. Is there anything wrong with the mix? or is that the inherent structure of it?
I am thinking of increasing cement and minimizing sand which I think is the cause of the weakness of the mix.
I am thinking of 2:1.5:1.5:1 - cement:lime:clay:sand. What do you suggest mates?

Mixing up very small samples sometimes results in a weak product. It's usually much stronger when you make a larger amount. Try mixing up around 4 L of the brew and skip the wool.

[v12spirit]

Re: Brick oven reconstructed to a steel one

The dome will be 5 cm thick. The sidewalls and the hearth will be 3 cm thick.

Because the upper steel belt is just 3 cm wide and I am not going to make any more modifications to the steel construction, a subtle emerged at the transition between the dome and the sidewalls. In order to make the dome come in full contact (conduction) with the sidewalls, I had to extend the refractory blocks constituting the sidewalls 3+ cm over the upper belt welded around the dome. Two approaches to achieve this:

The first is just to extend every refractory block along its contact surface with the steel. This implies making the extension "fly" temporarily, and lean eventually on the dome cladding rather than lean on the steel belt or the steel sidewalls as the case with the rest of the refractory block.

The second is to make the refractory block continue (in one single block) a little over the dome (a few centimeters horizontally and a few vertically) as if the block is bent along with the transition. This implies that the refractory block is engaged with the steel belt in a male-female engagement.

The second approach is more efficient for conduction because in the first one when the dome expands the steel belt will move the extension away from the dome cladding losing the contact between them, but the second may risk cracking the refractory block close to where it engages with the steel belt, and it may not because the expansion of the dome will make the steel belt move the whole block so the bent extension of the block will just slide over the steel dome. But just imagining the steel belt penetrating the refractory and wanting to break it is the nightmare I want.. Nevertheless, I am strongly tempted to go for the second.

The third option is just to keep the refractory blocks into the limits of the steel belt and not to risk any cracking. I will go for this option only when I am convinced that the first two do not make difference.

Below is a cross section of the oven illustrating the three cladding options.

Any suggestions?

[david s]

Re: Brick oven reconstructed to a steel one

I think you might be defeating your original intention of a fast heat up. 50 mm of refractory will take around 1.5 hours to heat up properly.

[v12spirit]

Re: Brick oven reconstructed to a steel one

I think you might be defeating your original intention of a fast heat up. 50 mm of refractory will take around 1.5 hours to heat up properly.

Right. But I think I'm still safe as for heat up time for these reasons
1- The steel will heat up very fast regardless of the thickness of the refractory over the dome. The thermal mass over the top of the dome will not affect heat up time in a noticeable way especially with 5 cm thick and the squirrel tail assist. It just stores heat for an acceptable heat up degrading.
2- There is a considerable reduction in thermal mass in the rest of the oven, especially the hearth. The hearth bricks are already over a steel sheet, the sidewalls are penetrated by 15 steel sheets that conduct heat into the refractory in addition to having one face coming in contact with it. The whole steel surroundings will prompt the refractory more than if the same refractory was alone.
3- When I wanted fast heat up time, I was implicitly seeking fuel efficiency. The experimental runs of the steel-alone oven showed unnecessary wood consumption when operating the oven for more than an hour; the oven was always starving for wood to keep hot while the added thermal mass could keep the oven hot once it clears more steadily. The effect of the thermal mass is very similar to the effect of the flywheel in an engine. It does add more inertia to the mechanisms degrading the performance somehow, but grants more torque output for engine rounds and a more steady operation.
I have a strong sensation that adding the same structure of steel to a regular brick oven without reducing its thermal mass does speed heat up time . With thermal mass reduction, more speed up would be achieved.
I'm not claiming that with the refractory the oven will heat up in less than 1.5 hours. But I claim that this oven with both of its steel structure and the reduction of thermal mass in the sidewalls and hearth will certainly heat up faster than if I were to reconstruct it with just regular 5 cm thick bricks, but to what extent? I don't know.

[david s]

Re: Brick oven reconstructed to a steel one

Right. But I think I'm still safe as for heat up time for these reasons
1- The steel will heat up very fast regardless of the thickness of the refractory over the dome. The thermal mass over the top of the dome will not affect heat up time in a noticeable way especially with 5 cm thick and the squirrel tail assist. It just stores heat for an acceptable heat up degrading.
2- There is a considerable reduction in thermal mass in the rest of the oven, especially the hearth. The hearth bricks are already over a steel sheet, the sidewalls are penetrated by 15 steel sheets that conduct heat into the refractory in addition to having one face coming in contact with it. The whole steel surroundings will prompt the refractory more than if the same refractory was alone.
3- When I wanted fast heat up time, I was implicitly seeking fuel efficiency. The experimental runs of the steel-alone oven showed unnecessary wood consumption when operating the oven for more than an hour; the oven was always starving for wood to keep hot while the added thermal mass could keep the oven hot once it clears more steadily. The effect of the thermal mass is very similar to the effect of the flywheel in an engine. It does add more inertia to the mechanisms degrading the performance somehow, but grants more torque output for engine rounds and a more steady operation.
I have a strong sensation that adding the same structure of steel to a regular brick oven without reducing its thermal mass does speed heat up time . With thermal mass reduction, more speed up would be achieved.
I'm not claiming that with the refractory the oven will heat up in less than 1.5 hours. But I claim that this oven with both of its steel structure and the reduction of thermal mass in the sidewalls and hearth will certainly heat up faster than if I were to reconstruct it with just regular 5 cm thick bricks, but to what extent? I don't know.

1. I can't agree. Because the refractory cladding is in direct contact with the steel it will be sucking heat from it resulting in a slower heat up for the same given amount of fuel put into it.
2. I agree because the steel is more conductive it should spread the heat into the refractory more evenly.
3. This is a very good analogy, but remember that the flywheel requires more energy to get it up to speed, or in the ovens case, up to temperature.

[v12spirit]

Re: Brick oven reconstructed to a steel one

1. I can't agree. Because the refractory cladding is in direct contact with the steel it will be sucking heat from it resulting in a slower heat up for the same given amount of fuel put into it.

Maybe I am making myself optimistic by Wiley's oven. It has a 1 cm thick steel dome, clad with a thick (I reckon 10+ cm) layer of cement and crushed basalt, without steel under the hearth, and is claimed to clear in 45 minutes.
I think the term "clear" is distinct from "saturate" especially in hybrid (steel-refractory) ovens; maybe because his oven's steel dome gets quite hot fast, the entire oven is benefiting from that. Tonyp's indoor brick oven has a 5" thick layer of bricks on the hearth and he showed the bottom of his pizzas finely burnt after 2.5 hours from lighting the oven. That is not far from ovens with 2.5" hearth bricks.
Myself was a big disbeliever in thermal mass trade-offs, but these guys are reporting practical information that I cannot ignore.
How long does my oven take to clear (or as I prefer to say how much wood to clear) is a question I hope I can report its answer soon.