Tandoor - issue with the clay liner

[Farooko]

Hi All

I bought a clay liner for a tandoor and fired it up. It was oki to start with like first 10 minutes and than I heard some loud bands and when I saw inside, the inner layer was peeling off. Please have a look at the pictures attached. I have two questions and would appreciate if some one could please help

i) Why did this happen? any ideas
ii) How can I repair this. I have fire clay available. Can I use that to fill the peeled off area?

[SableSprings]

Welcome Farooko! Was this a new clay liner? If it was, it looks like it had not been cured properly and there was a pocket of moisture or an imperfection that expanded when heated causing the damage. David S is our casting expert on the forum, but I don't believe minor surface damage like this can be easily (or reliably) repaired. Hopefully David will be able to give you some solid advice or better options. I'd be only able to suggest sanding/grinding it smooth and do some small fires for a couple days to make sure you don't have another problem somewhere else and then simply use it with those surface "imperfections".

Good luck...and go to your User Settings, Account, & about halfway down you'll see Conversation Detail Options with Show Signatures, Show Avatar, & Edit Signature. Choose the Edit Signature and put in at least your general location. That way, your general location info is always showing on-screen with your posts. Then if someone has local knowledge they can more effectively get that info to you....thanks in advance!

[Farooko]

Hi Mike
Many thanks for your response. Yes, it was a new liner.

Whats your opinion on using the fire clay for filling the gap?

I am going to update the profile as well now.

Thank you once again

[david s]

It sounds to me like it is a steam spalling issue. Usually that results in its shearing off from the centre ie it tends to split neatly from the centre of the casting. This is because moisture in the centre has too far to travel to the outside and the steam suddenly expands in the centre of the wall. Usually occurs at around 250 C. This is something every potter is well aware of when firing biscuit ware.
From what I understand Indian tandoor ovens are made from unfired clay reinforced with horse hair. If this is correct the oven must be dried very slowly until all the moisture has been purged. Repair now will be very difficult as wet clay will not bond to dry clay. In addition as clay shrinks considerably it will want to pull away from anything it is applied on to. You could try damping down the surface continually so the whole thing becomes moist, mixing 50%sand 50% clay into a plastic state (this will reduce shrinkage) Paint the surface to be repaired with vinegar to assist bonding the apply the mix. This then needs to be kept moist for at least 24 hrs. Then allowed to dry slowly at least a week before very slow drying with fire. Even following this procedure I think you’d be lucky for it to be successful. It is the equivalent of a potter attempting to attach a wet handle to a dry pot. If I’m wrong and the liner has already been sintered (fired to 1000C) this operation won’t work, you’d need to replace it. To test if it has been sintered rub the surface with water and if it gets muddy it hasn’t been sintered.

[Farooko]

Hi Dave

Many thanks for your detailed response. You are correct in saying that the liner is not sintered yet. I think I have only one option and that is what you have suggested i.e mixing the sand and clay and follow the process as per your response above. I have couple of questions:

- Can I use fire clay and sand mixture or do I need similar clay that has been used for the liner (terracotta clay etc).
- Or can I just sinter the tandoor as it is and see how it goes?

Many thanks

[david s]

Any clay should be ok. Different clays have slightly different shrinkage rates, but the addition of the sand reduces this to a minimum. Getting and holding sufficient moisture into the clay liner will be your greatest problem in achieving a good bond. Try a spray bottle filled with clean water. That way you don’t disturb the surface. The water will penetrate into the dry clay almost immediately. Keep rewetting it. You will have to refill the bottle a number of times.
You will not be able to sinter the liner yourself. It requires a kiln to take the temperature up slowly and evenly. Particularly from 500-650C where complex changes occur. This is not possible by fire in the liner. Apart from the uneven temperature issue you’d be lucky to achieve a max temp of 450C in an updraft tandoor.