added by admin: Hi Debbie, please fine all needed information about Vermiculite insulation information (in a way it can be replaced with ash for instance).

But I do not have sufficient funds for this work, and I should use very cheap materials to build my vertical charcoal kiln.

And I realized, that I can make main body shell of the furnace with 20 cm thickens from concrete.
But I do not know what materials I should use for the internal body of the furnace, which is stable against heat 1200 ° C.
Please suggest something that may be resistant to 1200 degrees Celsius temperature, doesn’t crack, don’t separate from the body of the furnace casing, won’t burn and oxidize and Most importantly, it will be very cheap to build.
Thank you very much in advance for your information.

added by Rado: Sepha, if you want to create the kiln out of clay and use your kiln for many years, it is a wise idea to build the inner walls of this kiln, the hot face lining, out of firebricks. Because these bricks last. Otherwise if it was just a test kiln you could also make it out of an old metal barrel for instance. You can use standard firebricks for raku and you don’t necessary need a large volume space inside. Raku pottery is fired in a much lower temperature than other pots,(some blue” Egyptian glazes require low temp. as well), you can achieve absolutely amazing glazes on pots in raku kilns. Look on web for Japanese raku pots images.

Are you planing to do the kiln outside with some arty like clay finish? Or mosaic? If that was the case, then leave a gap between the inner firebricks and the outer decorative skin. The inner part will be expanding as it heats up. If there wasn’t some gap space in between these two, the inside will push onto the outer part and, the movement would crack it. You can gradually fill the gap with the ash from firing. It will work as a cushion and if the gap was 2″ – 5cm plus wide then also as a heat insulation preventing the outside clay from getting too hot. I cannot wait to see images of some of your pots.

added by admin: Ah, thanks for the information. In this case the clay is added to the cement with sand for the mix holds in more water. If the work is slow etc., bricklayers add lime for the same purpose. The mortar sets in a lot slower time rate. I reckon about 3 times more slowly, lime can be quickly remixed once too in a wheelbarrow if needed. It will be the same with the clay. The Bentonite will stand the heat or a much higher heat but you don’t need to add that. In work with clays it’s used more for glazing, or for example also in mold making, molds from packed sand for casting metals where it helps the mold to face the heat, protecting the hot face. I think the clay adobes would become unnecessarily brittle, less porous and don’t know about its properties under continuous refiring and cooling down where you can get the cracks. Maybe a separated fire box made of clay would find a use for Bentonite, but that’s completely different oven firing concept not too suitable for small family sized cooking ovens whose are build out of clay or put together from clay adobe tiles. Try to lean towards putting your dome together from many adobe tiles in opposed to a large block segment or segments. It’s described more in this fireclay text above on the page.

added by admin: When you say sand with clay and concrete, the concrete; what do they mean, is a cement added into the mix or actual real crushed concrete like a sharp coarse or finer grog? What is the intended use for this clay based product, if the clay is mixed in, is there anything mentioned on the bag? What type of cement it contains? If that is a cement. Maybe a heat resistant cement? Otherwise it does seem there is only small amount of clay to reheat it for cooking many times.

I haven’t seen any brand for fireclay as such, it’s always called simply “fireclay” or “fire clay“. Pottery shops will have it as well, or they can show you a cheapest version of clay, clay body with coarse sand in it usually used for low fired pots, modeling or sculpturing. Ask them also for an old clay like that, when it’s packed in plastic for a long time it gets much drier so potters don’t want it anymore, usually these shops put it on sale to, literally, get rid of it.

And I also rediscovered a childhood love for mud. Fantastic!

added by Rado: Hi Jez,
Thanks for the comment, it’s suitable for this topic!

Have you tried adding plaster and Sodium silicate to test your mixes – Na₂SiO₃ (also called water glass or liquid glass). It’s not toxic, it is being used in refractories and for fire protection and also in food industries. You can mix it in a mix, also paint it on with brush or dip your fired items in it. If they are still porous clay, like firebricks and other low fired clay bricks (for example chimney and fire place bricks) for instance, the liquid gets absorbed into the body and protects then the hot face. Sodium silicate can be purchased in liquid form or in white powder form for mixing with the clay or cement, Na₂SiO₃ dissolves in water, stays clear like a clear lacquer. Sodium silicate will nicely bind solids such as powdered perlite you use and withstands the high heat. Email me some pictures of what you do! send to: pizzapaddle at gmail dot com