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what can i use, under the ovenfloor, heard of sand...
and for the covering, adobe with straw, cowshit, ...??
Sand is not an insulator - adobe with straw is usually made with high amounts of clay, which is not an insulator. Cow excrement is fertilizer, not insulation.
Insulation under the floor is critical if you want the oven to perform. Without insulation you won't get the oven floor temperature to stay hot, making it very tough to cook anything...
Use a good masonry panel insulation - one that can tollerate the 1,000 F temperature and the weight of the oven. Or use perlite or vermiculite - (mixed with Portland cement per the Pompeii oven construction instructions) either material is commonly available from masonry supply or agricultural supply stores.
If you skimp on the insulation you will end up with an oven that doesn't function well, so take the time to get this part right!
What they used 200 years ago, as well as 2000 years ago in Italy, was volcanic pumice. Works as a pretty good substitute for vermiculite, used the same way. I wouldn't use anything organic, like straw or cowpatties: at best it would char and stink the place up, at worst it might catch fire when it heats up. Also you want rigidity under your oven, sagging something this heavy and rigid is a prescription for disaster.
Hebel or AAC blocks are a fairly obscure item, at least here in the states
That's a pity. They are in fact very environmental friendly building materials compared to regular concrete and other construction materials. I hope they are available to him (in particular if his other choice is cow-shit!).
Without proper insulation, it gets very hot, and will bleed out the heat from the floor you need for cooking. My oven has two and a half inches of mineral wool board (HW insblock14) and the support slab remains cool to the touch at full pizza heat.
Hi Dan Qui,
I was wondering how your oven turned out. I think we face similar challenges--I am trying to build an oven in rural Uganda so obviously supplies are limited. On the suggestions people have given me, one suggested clay mixed with straw for insulation, and another mentioned that some earth builders use glass bottles (not broken I think for the airspace) in earth for insulation. Did you ever finish your oven? What did you end up using? Does it work well?
Broken glass is a proven no-go: it's as useless as sand as an insulator.
The whole-upright bottles is an interesting idea, it would maintain an insulating airspace. Maybe jars with straight walls would have more strength than necked bottles. Hmm. I'm wondering about air expansion within the bottles. If you could top the bottle/jar layer with a sheet of expanded metal lath, it would prevent air from being trapped in the bottles.
I've also heard the old fashioned product called "Expanded Clay" -- argille espanso.
I used this expanded clay balls in Spain James (BFB) and it is only so-so. Works, but still loses too much heat in my opinion. The BenjaMia Bakehouse Oven with the Pelite insulation is proving far superior with very little heat transfer.
I would not discount the mud/clay mixture though. I think that has been used for years. I saw a field oven at Colonial Williamsburg built that way. As long as you have an inner fireproof layer, like bricks or clay, I think you could use a high straw content outer layer with good success....especially in places like the amazon jungle!!!!
Sharing life's positives and loving the slow food lane