2 meter diameter New build oven with pumice reinforced with Basalt Rebar

[Alomran]

I have read in this forum various recommendations on the curing time for a lime mortar mixture of 3 sand : 1 Fire Clay; 1 Lime : 1 Portland cement. Some are with the idea of leaving 6-7 weeks for curing, others 2 weeks. I suppose the longer the better, however, what is the practical time for curing a dome with lime mortar?
Thanks

[SableSprings]

The reason some of us have installed a BBQ light (flexible neck light mounted outside the oven) is that when you are cooking without flame (like baking bread), it can be literally impossible to see anything in the oven after sundown. The beauty of a long neck flexible light is that you can keep it out of the way when it's not needed. As David S noted above, you are often baking by smell, sight, & experience and that's a great experience. It also keeps you much more involved in the real conditions process of cooking instead of leaning totally on a "...I know it smells burnt, but the recipe says to bake for 35 minutes..." approach. I get the biggest kick out of someone bringing food over to be cooked in our oven and they have a recipe that says something like "...bake at 425F for 10 minutes and reduce to 375F for an additional 40 minutes". They ask what the temperature is in the oven and I tell 'em it's right at 500F and it's going to be that temp for a while, so let's put this on a reversed cookie sheet and watch/work the food until it looks & smells done...that ancestor cooking with fire stuff

Back to the lighting--having both your hands free to poke the pork, work the peel, or turn the sheet pan is well worth having something "hands-free" available to illuminate the oven's interior. Having an assistant that holds the light and your adult beverage might even be better ...

When I first started making bread, I had a baking session where I put my loaves into the oven at twilight. When I went to check on their progress a little while later, I had to return to the house for a flashlight because I could not see anything in the oven. Even though I had some soft lighting in the oven area so I didn't stumble around, the lights weren't oriented toward the opening or bright enough to illuminate inside the WFO. The next day I bought a battery powered, exterior BBQ light.

Just some "be prepared" thoughts...

[david s]

you don't really need a light in your oven. Flame works just fine

When firing and cooking in my oven I'm often reminded by the fire of how we use these ovens in exactly the same way as our ancestors did. An electric light, or thermocouples for that matter, tend to severe that link with history. The more you use your oven the less you rely on gadgets.

That's probably the alcohol talking.

[deejayoh]

you don't really need a light in your oven. Flame works just fine

[UtahBeehiver]

This comes question comes up here and there periodically. To my knowledge, no one has found anything that will work inside the oven due to temperature and sooting issues.. Many have used light sources just on the outside shining in though.

[Alomran]

My oven is in a woodland and I have one extension cable that extends 12 0meters away from my home before getting to the WFO. Given the distance from my house, the area is very darek under trees, I am wondering if there any flood light that can installed inside the oven and designed to withsatnd high temperature?

[Karangi Dude]

If you recommend using it in building WFB, how long do you leave it for it to cure before you fire up the oven?,

There are different kinds of mortar that can be used, the common factor is there will a lot of moisture in your mortar and in the bricks being used
There are also a lot of other factors like where you are building the oven, is it under cover or outside where it will be subjected to rain etc.
If you have taken care not to let the oven get wet, I would suggest letting it dry by air and sunlight (covering it over at night) for a couple of weeks before starting your curing process
Alomran, there is a lot of discussion on curing on this forum and it is up to the individual to make a decision as to which is best.
My recommendation is not to use any flame at all by using heat beads / briquettes for several days, but as I said there is a lot of info on this forum about curing

Cheers Doug

[david s]

David, I am not going to use the pictured proferated terracotta on top of the heat storage bricks as I hadn't considered the uniform thermal mass. Instead, I will be using terracotta building bricks as a hearth. The fire bricks in the UK are expensive, the asking price is £1.65 for each plus 140 miles courier/shipping cost. This is why I have resoluted to using normal clay bricks and heat storage bricks. I have done an experiment on them and the building bricks I have seem to handle sudden heat rise as I put it on a gas stove for 40 minutes and it handled it very well.

There is a reason firebricks are recommended. You should get away with using solid reds (not sure about heat storage bricks) for the dome, but the floor is a different matter. Placing a brick on the gas stove for 40 mins is nothing like having a really hot fire over it for a few hours. Also doing it once will be no indication of long term serviceability. They may work fine for a year or two then start spalling. You may get away with them, but as they're not designed for a high heat application and there's no way of knowing their composition, the only way to tell is by trying them out. I suggest that if you want to go ahead with them, lay them loose on a thin bed of dry 50/50 clay/csand levelling layer, so they can be replaced if necessary.

[Alomran]

Alomran,

That all sounds pretty good laying clay bricks on there flats over the storage bricks should be fine, could you please clarify your intended wall thickness

Cheers Doug

The wall thickness on the soldier course was a blunder!. I was thinking of making a low dome rather than a sphere prior to reading your post and your published comments. My intention was to make a structural support for the loads spreading on the base of the low curvature dome on the base. At the same time, I did not have in mind the importance of the uniformity required of thermal mass. Only after you have mentioned it I became aware of it. The thickness the wall is 200mm plus I have added a clad of 70mm thick heat storage bricks facing inward to absorb heat and to reduce the huge diameter of the dome by a total of 140mm. Please bear in mind that i wanted to cook lamb and cook numerous dishes all at once when cooking for family and friends. I have been to Sardenia and saw this huge oven that they used to cook anything and everything with such flexibilty offered by the size of the oven. I am also keen on this Turkish meal that we had in Turkey and this is the real reason behind making the oven. https://www.youtube.com/watch?v=mWAuxL-ue0U
This is why I needed a large oven begging to point out that I live next to a forest with plenty of soft silver birch logs.
Cheers

[Alomran]

Because there are holes in those tiles they become less dense and more insulating. The holes will also reduce their strength and perhaps make them more vulnerable to cracking. You'll soon find out. I notice that some kiln shelves are now produced in the same way, not sure of their performance relative to solid ones, but the reduced thermal mass would be an energy saver.

David, I am not going to use the pictured proferated terracotta on top of the heat storage bricks as I hadn't considered the uniform thermal mass. Instead, I will be using terracotta building bricks as a hearth. The fire bricks in the UK are expensive, the asking price is £1.65 for each plus 140 miles courier/shipping cost. This is why I have resoluted to using normal clay bricks and heat storage bricks. I have done an experiment on them and the building bricks I have seem to handle sudden heat rise as I put it on a gas stove for 40 minutes and it handled it very well.

[david s]

Because there are holes in those tiles they become less dense and more insulating. The holes will also reduce their strength and perhaps make them more vulnerable to cracking. You'll soon find out. I notice that some kiln shelves are now produced in the same way, not sure of their performance relative to solid ones, but the reduced thermal mass would be an energy saver.

[Karangi Dude]

Alomran,

That all sounds pretty good laying clay bricks on there flats over the storage bricks should be fine, could you please clarify your intended wall thickness

Cheers Doug

[Alomran]

Doug, Thank you for your valuable advise stemming from experience. I have tried to remove the heat storage bricks and the first 2 broke into pieces as they are brittle and the gaps in between the bricks are filled with filling cement. Given that the heat storage bricks may contain asbestos, I think I will leave them as they are due to health hazard and add a thin layer of clay bricks on top to make the total of approx 110mm thickness so that it is equal to that of the dome wall/thickness.
Thanks again for saving the oven!

[Karangi Dude]

Alomran,

Try not to over think how these ovens are supposed to be when they were first built some 2000 years ago they did not have the materials that we do today they built them with whatever was available, they used things like sand as insulation which really is thermal mass except for the air in between the particles that acts like insulation so sand is neither a good thermal mass or a good insulation
There is basically two components thermal mass and insulation, thermal mass to absorb heat and insulation to help retain that heat
Any solid clay type brick is a good thermal mass the difference with a clay brick and a fire brick is that firebricks are a little more dense and don't react to thermal shock like clay bricks do
So a good Wood Fired Oven consists thermal mass and insulation under and over the entire oven
I my opinion I would remove all of the hearth material including the sand right back to the insulating material that you have used and replace it with firebricks if you can afford them or solid clay bricks laid on there side that will give you 115mm of thermal mass for your hearth
Also I would lay them in a herringbone pattern on a thin layer of sand say 5mm thick just to get them level

Cheers Doug

[Alomran]

Hi Alomran,

I see that you have used some sort of paver for the hearth it looks like it is only 40mm thick, it concerns me what you have placed them on is that a thick sand base? with an oven that size and with walls that thick I would suggest that your oven could be out of balance. Most ovens have walls 115mm thick and hearth 75mm thick, if you have walls 220mm thick then I would suggest that the hearth would need to be at least 115mm or 150mm. With your walls being so thick it will take a lot of time and wood to get the oven up to temp that would then make your hearth very hot in comparison the your walls and then you would have a problem with the hearth cooling to quick.
Alomran I have had some experience with larger ovens see; Karangi Dudes 48inch Oven (https://community.fornobravo.com/for...-s-48inch-oven) I have worked on and cooked in many kinds of ovens wether they be igloo or barrel ovens and the one thing that is most important is to have your oven balanced heat wise (having the right amount of thermal mass and the right amount of insulation for the walls and the hearth)

Cheers Doug

Thank you for this valuable logical advice. Perhaps, you have saved my project from failure with your paragraph to which I am most grateful.
Allow me to ask...I do wonder if the heat storage bricks that contain steel in it's ingredient are designed to store heat for a very long time would retain heat as long or even longer than the bricks I have used?
Given the heat storage bricks are 40mm and they are sitting on the sand bed,, do you suggest
1- Reducing the sand bed and increasing the Hearth thickness? or leaving the sand bed as it is but adding more hearth thickness?
2- Increase the hearth by the same thickness as the dome walls?
3- Can I add another layer of heat storage bricks or do you think this material is a fast absorber of heat and a fast emitter too and should use a slower heat absorber?

Alternatively:
I have a 3cm perforate terracotta clay tiles that I can add on top of the heat storage bricks with approx 1cm air gap, do you think this is adequate if the dome walls are half a brick thick?