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Building a tandoor - what type of clay to use and...


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#1 Mart

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Posted 21 February 2013 - 05:40 PM

(please, do not direct me to those awful "use a flower pot ..." DIY sites :) We like to build a small tandoor. I have seen a used oven clay pot but never a new one so I have no idea, are those pots just dry clay or actually fired in a kiln.
For start, my questions are:

1) What type of clay to use (I was thinking about low fire clay with lots of grog... not sure about the grog part)
2) Do I need to mix something else in to the clay?
3) Do I need to fire the completed pot in a kiln? (if yes, at what temperature)



#2 Iforgot

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Posted 21 February 2013 - 09:18 PM

I would use micaceous clay and fire to ^06 once
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#3 neilestrick

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Posted 21 February 2013 - 09:46 PM

A groggy terra cotta would probably work. If you want it a little less porous, take it up to cone 02 or 01.
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#4 Mart

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Posted 22 February 2013 - 03:19 AM

I am not from US so this cone business needs some calculations. As I understand it, cone 06 can be anything between 969-1023 °C and 02-01 can be anything between 1078-1178 °C depends what cones are used and so on. You guy do not make it easy :)
BTW, cones are meaningless over here. Not a single pottery shop sells "cones" (they actually sell very few useful things) and I have not met anyone who actually uses cones in electric kiln. Honestly.
I'll just get some local low fire groggy clay and use what ever temperature is recommended on the bag.

Cheers

#5 jennko

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Posted 22 February 2013 - 08:01 AM

Some good information about types of clay to use to build a tandoor oven



full article at http://www.nytimes.c...wanted=all&_r=0


Mr. Levy’s first innovation was to fashion the body from a blend of earthenware and stoneware, the former chosen for its modeling and expansion properties, the latter for its ability to withstand high heat without cracking. For porosity (an essential quality so that flatbreads can cling to the oven’s inner walls), he added finely ground fired clay, known as grog. For insulation and extra strength, he developed a clay and vermiculite mixture that could be baked onto the exterior of the pot.

#6 Marcia Selsor

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Posted 22 February 2013 - 08:17 AM

From my experience in Uzbekistan I'd say this oven is made from a refractory castable just by examining the construction and how it is built into the wall. There could possibly be a large ceramic pot built into a permanent position covered with a concrete type of material. The bread is baked on the wall til it drops. A ready hand catches it.

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#7 Mart

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Posted 26 February 2013 - 12:54 PM

Thank ya'll for taking your time to answer. I found some type of "fire proof" (no idea, what the correct translation is :) ) clay that withstands the thermal "shock" of temperature changes. I am going to build a small one out of this stuff and see what happens...

#8 Marcia Selsor

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Posted 03 March 2013 - 12:28 PM

From my experience in Uzbekistan I'd say this oven is made from a refractory castable just by examining the construction and how it is built into the wall. There could possibly be a large ceramic pot built into a permanent position covered with a concrete type of material. The bread is baked on the wall til it drops. A ready hand catches it.

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#9 Olesya

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Posted 09 March 2013 - 10:50 PM

Hello everyone,

If anyone is interested, I am posting a video of how tandoors are made in Uzbekistan and Turkey. One of them is however in russian, the other is in turkish, but i think the narration in this case is not important :






http://www.youtube.com/watch?v=CmwjqWdGgcQ


http://www.youtube.com/watch?v=f_ylzxtLGjQ

I too really want to build one, but I am far from being a specialist in ceramic and I do not know the terminology. I bought some firing clay and this is what was written on the label:

Albaster Fine Firing Clay.
Firing clay cone 04 to 2. Shrinkage of 8% and porosity of 4% at cone 02.


Do you think this material would be suitable to build a Tandoor?




#10 Mark McCombs

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Posted 10 March 2013 - 01:53 AM

Wonderful videos. Thanks for sharing the links.

I am curious as to what was the white, fibrous additive that was used at the end of the second (2/3) video.
Looks like it was used as a finishing coat on the tandoor.
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#11 Olesya

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Posted 11 March 2013 - 12:17 AM

Wonderful videos. Thanks for sharing the links.

I am curious as to what was the white, fibrous additive that was used at the end of the second (2/3) video.
Looks like it was used as a finishing coat on the tandoor.



I cant tell you exactly because I dont speak Turkish. But from what I can see it is cotton fiber. But I know for sure that in Uzebakistan, they add goat or camel wool to the clay. The wool is used to solidify the clay, so there will be no fissures. After, when the tandoor is fully heated, the wool will burn and you will be left with micropores that will help with the heat conducting in the oven.

Do you have any recommendations for the clay?

#12 Marcia Selsor

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Posted 15 January 2014 - 08:21 AM

I know in Uzbekistan they add cat tail weed fuzz into the earthenware when adding handles. The shredded stuff on the ground when they are building ovens could be wood shavings, straw, wool as you mentioned all would serve to bind and make porous.
Great videos.I loved the bread from these ovens and I have some tools for putting pinholes in the center of the bread to make it cook more evenly, less doughy.
I would think a raku clay body would work best for these, or one where you add something for the porosity


Thanks.

Marcia

#13 Norm Stuart

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Posted 15 January 2014 - 02:34 PM

Mart -

Since you buy your clay from Frankfurt, there's no reason you can't buy your Segerkegels or Ortonkegels (Orton Cones) from Köln or Dortmund.

http://www.reimbold-.../en/orton-cones

http://www.reimbold-.../ortonkegel.pdf

http://www.toepferho...segerkegel.html

http://www.marienfel.../segerkegel.htm

http://shop.keramik....ormalkegel.html

200837882011_2.jpg

 

You verify the total cone accumulation delivered by your firing program using the zeuge that the kegels provide.  http://de.wikipedia....wiki/Segerkegel

cones%20%26%20stand.gif

After all, they were developed by a German chemist, Herman Seger, around 1870.  But Ortonkegels are now really the only kegels used, even in Deutschland.

I am not from US so this cone business needs some calculations. As I understand it, cone 06 can be anything between 969-1023 °C and 02-01 can be anything between 1078-1178 °C depends what cones are used and so on. You guy do not make it easy smile.gif
BTW, cones are meaningless over here. Not a single pottery shop sells "cones" (they actually sell very few useful things) and I have not met anyone who actually uses cones in electric kiln. Honestly.
I'll just get some local low fire groggy clay and use what ever temperature is recommended on the bag.

Cheers



#14 Tyler Miller

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Posted 15 January 2014 - 02:42 PM

I would just use an earth-dug sandy-clay type mud, straw, and horse manure.  Roughly 75% clay, 20% straw, and 5% horse manure by volume.  Maybe substituting a lot of the straw for cotton, wool, or horse hair?  It worked for Quebec ovens, ancient and medieval kilns, and a few charcoal forges and remelters I've made.  :)



#15 indigav

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Posted 26 June 2014 - 12:13 PM

Hi all

 

As a total novice I hope there is still some interest in this thread as it's the only one I've found to date that actually talks about the clay used in making a tandoor oven.

 

I'm based in Manchester UK and have recently built a tandoor oven for charity out of a terracotta pot. It generated many conversations from the Asian population including how grandparents would have made these using clay mixed with the inners of old mattresses and a drum to house it. This has made me fascinated and I'm hoping to build a proper tandoor now using clay.

 

I've read the articles from jennko, and Tyler Miller; watched the above youtube clips and others I have found too. I'm left with a lot of questions still and before I ask them I'd like to point out that a cone is a shape which normally holds ice cream for me :) . I have no understanding of what they are other than that. Also from all the research I've done tandoor and clay/pizza ovens seem to be dried and fired outdoors using traditional methods, so I'm hoping my questions will be answered without the need for kilns or specialist curing/drying/proofing/firing (whatever the terms are).

 

My questions are...

What type of clay are we talking about here? There seems to be a number of clays mentioned, including those in the article from jennko.

 

Horse manure is like gold dust round here, so what could be used as a substitute and why is it needed?

 

How long would I need to leave a pot to cure? (I think I remember clay is cured then fired from my uni days)

 

Will the clay fire and harden from a normal fire (charcoal) as a tandoor will reach temps of 400 - 480 C?

 

Any help with answering these questions, and others I have for later, will be much appreciated by me firstly, then by those that eat from my tandoor later ;) . Thank you.



#16 oldlady

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Posted 26 June 2014 - 09:13 PM

indigav, you are correct about ice cream cones and they are completely different from firing cones.   I can try to explain firing cones to you and Mart. 

 

ceramic  materials are hardened from dry clay to something you are familiar with like a dish or bowl, by heat.  the process is called firing, not baking or cooking, firing is the correct term.

 

clay is so varied in its character that it can be fired at many differing temperatures depending on its content.  in times past the only way to tell if it was finished was to pull rings made of the same clay out of the hot firing to look at them.  several were used in each firing until the potter was satisfied that the pots were finished. this was a judgment made by an expert based on experience. 

 

to standardize the process, something was needed that would be consistent no matter who was firing the clay. the hardness of  various clays was tested and their ideal melting temperatures were then known. temperature is not the only factor in hardening clay into a ceramic item, the amount of time it is heated is also important.

 

so, combinations of known clays blended together in the correct proportions are used so a pot can get to its ideal finishing point in the firing and not be heated to the point where the clay melts into a useless puddle. these blended clays are shaped like tiny solid triangular ice cream cones, and were invented to tell when a particular temperature was reached after a sufficient amount of time had passed.  these cones were assigned numbers to identify the proper time and temperature for a particular clay, so a potter would know that the clay item had been sufficiently hardened to be used for whatever purpose the item was made.

 

that is why we in the US refer to a clay as a "cone 6 stoneware or a cone 10 porcelain or stoneware" or whatever cone is the correct finishing point for the hardening of the pot. 

 

many of us use electric kilns which have a method of holding the cone in a position that allows the electricity to turn off automatically when the cone bends.  if you look at the Norm Stuart post above, you will see a drawing of 3 of these cones in a holder at the bottom of the post.  these cones have melted in a firing and show that the correct temperature and time have been reached.  three cones are used so the potter knows that the first (guide) cone, which has totally melted over the end of the holder and the actual (firing) cone the potter wants to reach have melted properly in this firing.  the upright (guard)cone at the opposite end of the holder has not melted so the heat has been just right and not so hot as to melt this higher temperature cone.

 

I am sure you could read a better description of how to use cones at the website for the ORTON brand cones which we use here.  SEGER cones are European.

I submit this information in an attempt to explain what must be totally confusing to someone unfamiliar with making pottery and hope my simplification is not insulting to others.


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#17 Tyler Miller

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Posted 27 June 2014 - 02:15 AM

Hi all

 

As a total novice I hope there is still some interest in this thread as it's the only one I've found to date that actually talks about the clay used in making a tandoor oven.

 

I'm based in Manchester UK and have recently built a tandoor oven for charity out of a terracotta pot. It generated many conversations from the Asian population including how grandparents would have made these using clay mixed with the inners of old mattresses and a drum to house it. This has made me fascinated and I'm hoping to build a proper tandoor now using clay.

 

I've read the articles from jennko, and Tyler Miller; watched the above youtube clips and others I have found too. I'm left with a lot of questions still and before I ask them I'd like to point out that a cone is a shape which normally holds ice cream for me :) . I have no understanding of what they are other than that. Also from all the research I've done tandoor and clay/pizza ovens seem to be dried and fired outdoors using traditional methods, so I'm hoping my questions will be answered without the need for kilns or specialist curing/drying/proofing/firing (whatever the terms are).

 

My questions are...

What type of clay are we talking about here? There seems to be a number of clays mentioned, including those in the article from jennko.

 

Horse manure is like gold dust round here, so what could be used as a substitute and why is it needed?

 

How long would I need to leave a pot to cure? (I think I remember clay is cured then fired from my uni days)

 

Will the clay fire and harden from a normal fire (charcoal) as a tandoor will reach temps of 400 - 480 C?

 

Any help with answering these questions, and others I have for later, will be much appreciated by me firstly, then by those that eat from my tandoor later ;) . Thank you.

The exact clay used doesn't really matter, and for a traditional tandoor, it likely varies quite a bit from location to location.  Any grogged terracotta will do the job just fine.  I would look for a terracotta advertised as being for sculpture.  I would then wedge in any of the fibrous materials mentioned like they do in the videos above.  If you want to go truly authentic you could try to track down a clay seam out in the country, but that's not always the easiest thing to do.  If you can't find horse manure, you'll likely have a very tough time finding usable clay.

 

Horse manure would add a fine-grained fibrous material that would function like the longer/larger fibers of cattail fuzz, wool, horse hair, etc. but different.  Think of it like mixing concrete--in order for it to be strong, you need gravel, pea gravel, and sand in addition to your portland cement.  In historical cob, and wattle and daub construction, the horse manure was actually a beneficial contaminate from the mixing process--guess what animal did the mixing.  It's not necessary, but if you can find it, a little mixed in would help with the strength during drying, and the insulating properties after firing.  If you can't find any and REALLY want to use a substitute, I recommend looking into making some paper clay.  The paper pulp would have very similar properties and you could likely replace it will all the fibre involved.  

 

The pot needs to dry for as long as it takes.  Sometimes this is days, sometimes weeks.  It depends on temperature, humidity, as well as the nature of the clay.  Generally more porous and coarsely textured clays dry faster.  A good rule of thumb is to touch your cheek to the clay.  If it feels cold, it's still a little wet, even if it feels dry.

 

The clay will not harden sufficiently at charcoal temperatures.  At 480C you're driving off the molecularly bonded water, but not much else.  You need to go higher to get things hardened.  Firing a tandoor is going to be the biggest challenge you face.  Very few people have the facilities to fire such a big chunk of ceramic.  Luckily, you don't have to fire too too high, cone 010-06 would work fine, the lower cones may even give you greater thermal shock resistance.



#18 Biglou13

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Posted 27 June 2014 - 08:21 AM

Start video at 2:50. Sawdust kiln made with insulating fiber

I'm interested how they are fired in countries of origin.
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#19 CarlCravens

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Posted 28 June 2014 - 10:37 PM

Auto-play videos in forum threads threatens your status on Santa's "good" list.


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#20 Babs

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Posted 29 June 2014 - 12:15 AM

I am not from US so this cone business needs some calculations. As I understand it, cone 06 can be anything between 969-1023 °C and 02-01 can be anything between 1078-1178 °C depends what cones are used and so on. You guy do not make it easy smile.gif
BTW, cones are meaningless over here. Not a single pottery shop sells "cones" (they actually sell very few useful things) and I have not met anyone who actually uses cones in electric kiln. Honestly.
I'll just get some local low fire groggy clay and use what ever temperature is recommended on the bag.

Cheers

Where are you Mart? No Cones??? can't imagine relying on temp. alone!






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