Fireclay sand required for a diy tandoor

[dexter7205]

Hello Members,

This is my first post here and my knowledge is low about the topic. Please go easy :-)

Background

I built a diy tandoor a few years ago(using popular instructions on youtube) and used it very often until the pot broke and vermiculite started dripping into the charcoal area. I disassembled it and next attempt with terracotta pot did not last long either.

I found some bentonite kitty litter clumping clay and built another one by hand(mix sand + bale) but that did not take any load. I learned later that bentonite is not a good clay for this since it retains too much water.

Fourth attempt

Trying to follow instructions on https://imperpro.ru/en/tandyr-svoimi-rukami-55-foto-sovety-po-stroitelstvu-i-ekspluatacii-delaem/

I got kaolin clay a couple 50# bags. But i do not understand what the writer means in the article by fireclay sand. The clay stores i contacted sell fireclay and sand separate. Do they mean Grog? 

Quoting from the above article

"To get started, prepare the necessary materials:

• kaolin (aka chamotte clay);
• fireclay sand;
• sheep's wool - you can take camel, if, of course, you can find it;
• an ordinary wooden barrel;oil - vegetable is suitable."

Questions:

• Which fireclay or sand mixture can I use? 
• If sand is needed, do i use all purpose sand or play sand?
• Sheep's wool is difficult to find here, camel hair is even more difficult. Is bale hay/straw a good substitute?

Thank you for reading my post this far. Appreciate your time/input on this.

 

 

 

[glazenerd]

Hi Dexter;

Your tandoor is a version of a rocket stove (google).  You are dealing with expansion (heating) and contraction (cooling.) In this case: low thermal expansion.  The silica sand is typically 30-40 mesh (Home Depot) is to help control expansion by creating voids in the clay body; for the same reason sheeps hair is used. The hair will burn out, leaving voids. Voids will absorb expansion that would normally cause issues in traditional pottery. There is a simplier way to get there: find the lowest expansion commercial clay available; these are normally sold as "ovenware" bodies.  Grab a bag of charcoal; yep, the BBQ stuff. Grind up the briquettes into a powder (wear a mask, outside). 30-40% is typical. For easy math- a 25lb bag of charcoal will do 75lbs of wet clay. When fired, the charcoal burns out, creating voids. Same principle, same result- much easier.  

Tom

[Callie Beller Diesel]

Hi and welcome to the forum!

I think a bunch of your confusion is coming from the quality of translation, and some unclear definitions used on the website you’re referencing.  It’s also important to note that since clay is found just about everywhere, it’s usually not worth it to ship it across the globe. They’re using materials that they have available to them that won’t be available in California. But there will be something with similar working properties that we can backwards engineer. There may not be that exact kaolin available to you, but there will be some kind of kaolin. 

So for some quick definitions: 

Kaolin: a category of smooth, white firing clays that are very refractory/not melty, and that can have varying levels of plasticity depending on the deposit/brand/amount of processing it’s been through. Not very many iron or other metal/flux impurities. It’s usually the basis for porcelain. For the most part it is sold as a fine powder in North America, but coarser versions can sometimes be had. EPK tends to be cheap and plentiful here. 

 Fireclay: another category of refractory clays that are generally not very plastic. It has a coarser particle size than kaolin, but not usually found in a mesh that we would call sand in North America.It can contain lots of secondary materials. Uses include brick making, some specialty firings, clay bodies that are used to make large pieces, or for making industrial refractory materials like crucibles. The fireclay sand mentioned may have been a material available in the website author’s location that made sense to use.

Grog: fired clay that has been ground, and sieved into varying particle/mesh sizes. Related: Chamotte clay is a refractory clay used throughout Europe as a clay body, and is also fired into grog, and then mixed into the unfired stuff for building large garden pots or tiles with. Chamotte may refer to the grog, the raw clay, or the mix of the 2, depending on context.

Sand: some kind of ground rock. Chemical composition, and therefore what temperature it melts at depends on the parent material. For your purposes, I’d get silica sand or grog from a clay supplier. Play sand from the hardware store could be made of something that melts, like feldspar.

Note also. All clay shrinks when it dries, some more than others. Shrinkage, and the resulting movement, can put stress on a piece that leads to cracking. Especially if the piece is dried unevenly. In general, clays with smaller particle sizes will be more prone to shrinking than larger mesh clays.

The writer of that website is pretty serious about getting a good oven that’ll withstand a lot of thermal shock when finished, and be able to survive a drying process without cracking. So the clay body needs to be considered a bit like concrete: a mix of particle sizes (fireclay/sand/grog) mixed with finer clay (kaolin) make a stronger end product. You wouldn’t want to use clays  with a really fine particle size like a bentonite or ball clay, because both of those shrink too much in the drying.

 I disagree about the charcoal being a good substitute for the wool if you’re using this method. The wool fibre is used not just for the insulation voids it’ll create when it burns out, but also because the wool will reinforce the clay like fibreglass. That will  prevent a LOT of shrinkage related cracking, especially if you’re working with non-plastic clays. If you can’t get wool, you could try another organic fibre like some kind of long, fine hay or grass. Common wheat straw looks likely to be too thick. In a pinch, you could even use shredded paper, or paper pulp. If you do use cellulose, don’t leave the slurry to sit for weeks: it’ll rot, and the smell will make your eyes water. There are ways to lay the slurry out to dry in days instead.

 

[Mark C.]

a ovenware body is now  sold by Laguna clay in so-cal-maybe clay planet in Bay area carries it. Try them as you are close.

Thats trhe best body for thois type of use as Tom point out.

[dexter7205]

Thank you for your responses and clarity provided on the topic. 

glazenerd -> I saw the video on youtube for a camp rocket stove using clay. I already bought EPK kaolin from east bay clay in richmond so clay part is settled. Thanks for your advice on bbq charcoal. Is that a substitute for fireclay or wool? It is readily available for sure. Also I am thinking of substituting grass hay for wool. 

Callie Beller Diesel -> yes the language and only a few pictures available(no video) on the article was confusing. I did get a couple bags of EPK so i am set with the clay now. Also based on your response it should be fine to use grass hay as substitute for the wool. I can also get a bag of raw sheep wool(https://www.amazon.com/USA-Fabric-Store-Stuffing-Spinning/dp/B0999RY7LL/ref=cm_cr_arp_d_product_top?ie=UTF8).

Yes the article might have used sand/fireclay/grog mixed with kaolin for the build. I do have kaolin now. For the remaining ingredients:

1) I can get a bag of silica sand. Or can I use all purpose sand.
2) fireclay part still confuses me. Home depot in martinez has https://www.homedepot.com/p/H-C-Muddox-50-lb-Fire-Clay-Concrete-Mix-100011882/100321936 . Is this okay for the application.
3) Grog, Clay planet in santa clara suggested https://shop.clay-planet.com/grog---20mesh.aspx . What do you think?

So how does this sound:

1 part kaoline clay +
2/3 each of silica sand, fireclay and grog. 

Use a combination of wool and fine grass hay.

Mark-> Thanks, this build i will go with kaoline clay as i already bought it, but i will check out ovenware clay.  Probably you are talking about https://www.lagunaclay.com/product-page/flame-ware.

Again, Thanks for guiding me through.
 

Edited April 19, 2022 by dexter7205

[Min]

Clay heating chambers/ovens have been made for thousands of years in many places around the world using simple local materials. Can't help but think a simple earthenware clay mixed with local sand or even quarry dust plus whatever sort of dried material was on hand would be what was used. Could mix up a custom blend of clay, grog, sand and combustable dried material but I don't see the benefits of that. Would be far less work to return the 2 bags of kaolin and pick up a few bags of dry mix earthenware to add the sand/grog/fibre. I'ld also make up a small scaled down version of what you are planning to try out before making a full sized one. 

Since these tandoors/ovens are not going to be fired up to temperatures that would involve the fluxes in say a cone 5-10 flameware or ovenware body I don't see the point of using them. Yes these clays are low expansion but since they won't be fired to maturity I kind of doubt that will come into play.

 

[Callie Beller Diesel]

Home Depot won’t show me the price for that bag of fireclay, but yes, that’s the kind of stuff they’re talking about. The only recommendation I’d make is to compare cost to the stuff from your ceramic supplier.

After going over this in daylight while having enough caffeine in my system, I took a second look  at the first tandoor design you tried and googled a few of my own. I have some ideas on how to simplify this for you. 

The first oven you built isn’t a bad design, the weak link was just the cheap terra cotta flowerpot. If you built a better liner pot, you could make an improved version of the tool you’re already used to using. 

Take the epk back to East Bay and exchange it for a couple of 50lb DRY bags of a Laguna raku clay. Tell them exactly what you’re doing with it, and they can recommend which one to use, as they have a couple of versions. That clay is already pre-mixed with grog and everything, and has the properties you’re trying to recreate. I have used that brand myself, and can confirm that it’ll build big pieces that withstand thermal shock, and it’s easy to add fibre to, if you get the dry mix.

Edited to add:

As far as the wool goes, it only matters that it’s a fibre. I happened to notice when I checked the link you included for that material that amazon suggested a loose cotton fibre for half the price at the bottom of the page. That would also work. 

In terms of how much fibre to add, I’d wet the fibre first, and lay it out on top of the bucket in a 1” layer, and mix it in by hand until it feels right, especially if you go with a longer fibre. If you try and use the drill, it’ll just get tangled in the bit.

[glazenerd]

Dexter:

perhaps I should explain the chemistry behind charcoal. The briquettes become granular when you crush them- 1/16, 1/8, 1/4": which acts as the grog to give this simple mix the strength to form. This is the reason grog, straw, and hair is not necessary. Rocket stoves are typically 1 1/2" thick: self supporting when formed. Oven ware bodies are primarily ball clay; that utilize low expansion fluxes (lithia/magnesium), not potassium/sodium used in cone 3 and up. Magnesium has a low melting point as well. Secondly, unmelted silica is highly expansive: so oven ware (and raku) swap out pyrophyllite for silica additions to help control expansion. However, kaolin is a poor choice for this type of project. The green strength of kaolin (porcelain) hovers around 400 psi, while ball clays approach 800 psi. 

T

[Mark C.]

WC 440 is the flameware clay it can be fired to cone 5-thru 10. The lower temp range makes it more open -better for your use.

By the time you have made 2-4 of these a big green egg may have been cheaper?

[dexter7205]

Thank you all for responses. I am learning/googling about each line you write. It keeps me away from work and I starting enjoying this project more.

Min -> Due to some kid issues at home, i did not want to drive couple hours for the clay. My next attempt(after this kaolin) will be the Laguna raku clay. There is so much knowledge here in this forum, not on internet. The article I shared is the only reference i found to build this kind of oven with commercially available materials. Senior members in my family back in india suggested to look for light brown soil + some soil from near a pond. I do not have an eye for that, but may be over time i will grow some 0-0 :-). 

Callie Beller Diesel -> Thanks, replacing kaolin isn't an option for me right now due to kid issues(couple hours drive). The clay shops i spoke to earlier had no clue about making an oven. This forum is the best knowledge i see. I agree the idea is to build a good pot that will last for longer time. If it cracks and i can fill the cracks, even better.

Another lesson (different from the pot) i learnt in earlier build is to make the pot a little elevated and sit on bricks. So i can put a grate and charcoal does not sink in it's own dirt.

I did get a bag of fireclay, it was 7$s. Going to get the cotton fiber too. So the coming weekend, I'd be babysitting and getting my mix ready. 
One part kaolin + 1/3 fireclay + 1/3 silica sand + fiber

Glazened -> Once this project goes through i will add pictures and steps so others can benefit. I'd have to go with kaolin for now but I'd keep your input for next time. Google search says Ball clays are 20-80% kaolinite. And EPK has high green strength(as mentioned on description), but i could not find a number. 

Mark C. -> Next attempt, if i need to for that clay. Yes, i think i have spent upwards of 200 already with all the attempts. Smaller version of that grill may be near the cost, but i did recoup some as the first tandoor oven was used for few years. At this point, it is more about getting it right and learning in the process.

Edited April 21, 2022 by dexter7205

[Pyewackette]

@Mark C. You can't do proper tandoor in a Big Green Egg.  The naan won't stick to the metal!  Or if it does, it'll burn to a crisp before it can bake.

Edited April 21, 2022 by Pyewackette

[Min]

2 hours ago, Pyewackette said:

@Mark C. You can't do proper tandoor in a Big Green Egg.  The naan won't stick to the metal!  Or if it does, it'll burn to a crisp before it can bake.

Inside of the Big Green Egg is ceramic made by Dal-Tile. Same company that bought up the old talc supply. Don’t know if naan would stick to the sides of it or not, if it’s too vitrified I kind of doubt it.

 

[Min]

12 hours ago, dexter7205 said:

Senior members in my family back in india suggested to look for light brown soil + some soil from near a pond. I do not have an eye for that, but may be over time i will grow some 0-0 :

Yup, local red clay, otherwise known as earthenware.

[Mark C.]

Ok I got side tracked that Green egg is a BBQ-I lost it in my mind about the OP making their 3rd tandoor . 

We get a lot of the make you own BBQ and make your own tandoor over the years here

Either way I'm will bill on the flame proof clay-its made to take this uneven heating and i the long run cheaper -the main issue is how to get it fired t begin with being so large 

But thats an issue no matter what they make it from. I suggest pit firing  it to firm it up. it would take a slow fire to do this as its to big to fit into an electric kiln (my car kiln could take it ) Of course I do not do that sort of thing as a professional making pots full time. 

The pit option is slowly bring it up with sawdust or straw or charcoal then wood. Its all a C--p shoot anyway the key point is SLOWWWWW heat

 

[Min]

1 hour ago, Mark C. said:

the main issue is how to get it fired t begin with being so large 

Traditional tandoors are not kiln fired. They are fired so to speak with  wood/charcoal, same as how they cook but won’t get hotter than that. Commercially made tandoor type ovens are kiln fired. Perhaps this is a question we should have asked early on in this thread. I assumed the tandoor wouldn’t be fired in a kiln, that was the reason I didn’t think an ovenware or flameware body would be beneficial as the fluxes wouldn’t have much effect if only fired to at the most around 900F.

[Mark C.]

Ok I assumed it would be kiln fired and that was a huge issue on size. I still go with the ovenproof clay pit fired-ending up with a better product.

[Pyewackette]

5 hours ago, Min said:

Inside of the Big Green Egg is ceramic made by Dal-Tile. Same company that bought up the old talc supply. Don’t know if naan would stick to the sides of it or not, if it’s too vitrified I kind of doubt it.

 

LOL!  I thought that was some kind of enamel!  Not being the bbq sort.  I'm good with squishy ribs out of the sous vide then bakened in an oven a little bit.  Barbaric, I know.

So no.  We want this:

Not this:

THIS:

Not this:

BTW:  How to cure a tandoor.  Or at least that's what these guys claim. That may actually be a stone tandoor, not sure.

OOO 'eck, that may even be cement or something. Plus jes pitchers there, here are the actual curing directions for whatever those mobile tandoors are made of.

EDIT: Yah yah yah.  Clay after all:

Quote

You must prepare the tandoor’s clay portion once before starting it for the first time. This seal and treats the clay, which in turn extends the life of your tandoor.

 

 

 

Edited April 21, 2022 by Pyewackette
I just could NOT get that link to go in right!

[Mark C.]

Ok -Arthur Brown and I go way back thanks for the reunite as I have missed him for 35 years at least.

Whats holding those pizza breads to the wall in your photos -either the thing is spining fast  (like the carnival ride where the floor drops out and you are stuck to the wall as it spins) or the dough is like a wet mud glod stuck to the wall as its fighting gravity well

bread is stuck to wall like these folks

 

Edited April 22, 2022 by Mark C.

[Callie Beller Diesel]

@Mark C. the dough is quite sticky, and the wall of the tandoor is screaming hot, and seasoned with oil like a cast iron frying pan. It cooks in moments. If you do meat skewers in there, they come out very tender.  Something about very high radiant heat. 

[Pyewackette]

Tandoori naan are cooked by being slapped onto the screaming hot sides of a clay vessel with fire at the bottom just as shown in the video and pictures.  It cooks fast and they snatch them out of the flames before they fall off and burn up in the fire.  I have no idea how they manage it.  The tops have spots of char and they are properly cooked through when done right.  Oven baked naan are just not the same. When they slap them on there the dough stretches a little which is why you get that sort of "tab" at one side (usually, not sure how they kept them round in the other picture). They fake that tab on the prepackaged ones.

I know from Indian food.  Trust me on this.  Pretty sure the OP does as well.

[dexter7205]

So the walls of the tandoor are seasoned with either yogurt + sugar / mustard oil + jaggery + some combination of spinach/grass. I was told that it lets the bread stick on the sides better. The temperature I recall in my first tandoor had to be 375 F + . I used to put water on one side and stick to the terra cotta pot on that side. If tandoor was hot enough it will cook in a minute or so.  I used to take it out with a pair of tongs. restaurants use something like attached picture. If the walls of tandoor were not hot enough the bread will not come off and it's a mess.

Attached some pictures. I had put stones on vermiculite later.

 

 

Edited April 22, 2022 by dexter7205

[dexter7205]

I mixed up 20lb each of epk, silica sand(industrial sand) and fireclay in a tub. Mixed it first by hand then with a drill+ cement mixer attachment. Per the instructions, i have to let it sit and take out water as it settles. I will add wool tomorrow as I receive it.  Please help with tips, pitfalls i should be aware of. As recommended i'd do a small template first

[Callie Beller Diesel]

The only thing I’d keep an eye on is the length of the fibre. If it’s long, you may just want to mix it in by hand rather than with a drill. I can see an overly long fibre just getting bogged down on the shaft. 

If it’s really, really long, there were some images on the first website you posted of the builder soaking the carded wool lengths in the slip to create sheets or slabs to build with. That seemed like a good way to work with the materials rather than against them. 

[Pyewackette]

Now I want one of these too ...  Keep us posted!

[dexter7205]

I could not work last weekend on the project. But i mixed some hay(fine) 1 inch in the mix. I have been taking out collected water and mixing periodically as well. 

I am facing an issue with the mix, it is too sticky, very difficult to get it off my hands. I need to make an inch thick rectangular pieces from it as suggested in original article. What can i do to make it work better. I was thinking of using some sand in my hands.