12. Repairs!

My clay oven is now almost one year old and, to be honest, it was starting to look it!

The last time I fired her up I noticed that the cracks in the outer layer had grown substantially and, disaster upon disasters, the following day I noticed what I thought was steam streaming out of a crack at the back.  In fact it turns out that the oven was on fire!!  It seems the cracks in the outer layer had penetrated deep into the insulation layer which, happy with its new source of oxygen, subsequently caught fire.  After dousing the smoldering mass with water I decided it was time to do something about it.

This week I repaired the broken chimney (see photo) and filled all the cracks with a new load of sand/clay mixture. There is nothing difficult about this.  Just make up the mixture as per the usual method.  Remove any damaged/friable bits of your oven.  Wet the area you are working on so that the new mixture can bind to the structure more easily. Mould and fill cracks as required.  Simplicity itself!

I have fired the oven since repairs and of course cracks re-appear (part of the normal expansion of the oven) but hopefully it should extend the lifetime of the oven a while longer.  We’ll see!

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40 thoughts on “12. Repairs!

  1. HI Simon. just a couple of questions. i just built my oven and fired it up. i’ve noticed a hairline crack from the top of the door to the top of the oven. Should I be concerned about it? i have lots of clay and sand left over, so if it’s only a matter of sealing it up I can do that. I made two layers, one base layer and the insulation layer. I may have erred, however as I made the insulation out of sand/clay and not just clay and water, and used pine needles as insulation. My bigger concern is the bricks for the oven floor…they exploded! They weren’t fire bricks and so I thought they were fine, but obviously not as they cracked and broke apart. Is it possible to make a layer of clay/sand and used that as my floor? My plan is to just brush out any broken pieces and layer it with more clay, filling in the holes.

    Thanks for the help


    • Hi Peter

      the hairline crack is not a problem. Fill it with sand:clay mixture and don’t worry about it. These ovens do crack when you fire them – they have to in order to accommodate the expansion. I can’t see that the insulation material you used would cause any issues. I’m more worried about the floor. I have never heard of this happening before. I always use normal bricks in my ovens (i.e. non-fire bricks) and have no problems. Maybe the bricks you used where weak, or maybe saturated with water? If there are only a few holes, you might be able to fill them but I fear that the material will constantly need replenishing. If the floor still works, i.e. you can cook on it and get things in and out easily, then it might be OK.


      • yeah it’s a mess. the bricks I used were from an old chimney, but they were the kind that have a few holes in the middle of them. Perhaps this created an air pocket or something, I don’t know. I
        I’m going to brush everything out in the next day or two, then i’ll assess the situation. I have a couple of round pizza stones that I may put on top to see how things go. It may just be ok to cover it up. It’s really weird, we can hear them popping and then pieces of brick comes flying out.


  2. Hi Simon, I am from India ad its a little difficult to find clay sand in the western India, However, I did manage to get some but I am not sure if its clay or something close to clay. I did make a cast of 4″ thick and i let it dry. But during the process of drying from the inside(by burning wood), there are 1cm cracks all across the dome. I am also running short of clay. However, I want to ask you
    1. what should the insulation layer typically consist of? what should its thickness be?
    2. Do I need to put another clay layer over the insulation layer?
    3. Do I need to fill the cracks before insulating the dome?
    4. I did try to putting some pizza sauce on bread slices and top it with mushrooms and olives but the toppings did not cook? is it because, the oven did not gain temperature due to the missing insulation layer?
    5. Can you list down some sites or blogs where simple methods are laid down to build the oven?


    • Hi Preeti

      1. If it’s cracking then you might want to try adding more sand to the mix. It’s the clay that contracts and forms cracks. Also, if it’s warm enough, i’d allow it to dry naturally.
      2. Insulation layer can be anything material with insulating properties, mixed with clay. I use wood shavings. You can use sawdust, newspaper anything. Just make sure it is fully coated in clay-slip otherwise it’ll ignite when you fire the oven.
      3. Yes, if you insulate then you need another clay sand layer. It keeps the oven hot but also prevents insulation layer combusting.
      4. I would fill the cracks before insulating. If it is badly cracked – I’d start again.
      5. Sounds like your oven wasn’t hot enough to cook the pizza. These ovens, when firing properly, will cook pizza’s in minutes.
      6. The instructions on how to build are all here, on this blog!

      best of luck


    • yes the bricks were wet. they were actually kind of imbedded in the ground, so probably absorbed a lot of moisture. Haven’t tackled trying to fix it yet, not really sure what i’ll do. Not the end of the world though, I don’t think.

  3. hello simon ive recently finished my second pizza oven the first was a disaster as i found a 80cmx60cmx8cm piece of polished granite when i was excavating a fosse septique in my village in france and thought it would be great to cook my pizzas on fatal mistake as it cracked completely even though i have granite slabs at 1.5cm thick for a conventional oven for cooking steak so had to demolish it and use refractory bricks instead my oven is a month old now and i have cracks like yours if not worse on the outer layer which i used common sense and filled them up with the sand/clay mixture also i noticed small cracks inside which doesnt really bother me as i dont think it will move open due the weight of the other layers im thinking of the chicken wire idea and a fourth layer what do you think? as repairing after every use is not really practical but i did have 10 friends round last night and we all had a pizza each and chicken wings and of course a few bottles of vin rouge so id like to thank you for your time putting these instuctions on the web and making my pizza nights possible

    • I think you have to make a decision about whether you are happy to live with cracks or not. These ovens crack – simple fact. Mine is in a pretty sorry state at the moment; cracks, broken chimney, a few raised bricks in the floor. I will patch it again this week but it is working just fine – perfect pizzas on Saturday. If you have the space then you could go for a fourth layer but I suspect this will also crack eventually. My own thoughts are, as long as the oven maintains it’s structural integrity, don’t worry too much about it. One day I’ll need to build a replacement and I can’t wait!


  4. Hi Simon

    I have just finished my 1st layer yesterday and when I got back from a friends this evening there is an almighty crack right over the centre! It’s so big I can almost read the print on the newspaper underneath! The sand is still in what can I do? Is it because it is too thin? Or has it dried too quickly? I am using a mix of Potters clay and sand. Any help would be appreciated


    • Hi Adam

      Maybe the layer was too thin or maybe your mix had too little clay in it. However, don’t panic. Pack the crack with more of the sand:clay mix and, if you can, cover it with a tarp and let it dry more slowly (a tip from another blog viewer).


  5. ok i dont no where to put this question as there is no genral enquirey box . but here goes has any one tryed paper brick logs for fuel in there oven if so do they work ? and do they leave a strange taste in the food ?ive been doing a bit of reacerch on this and aparantly its the more green option to wood using old newspap[ers just wondering if it works

  6. perche’ sopra il forno non fate un ultimo strato di argilla stabilizzata con la calce idrata e sabbia e poi e sempre meglio” armare ” l’argilla con della paglia che serve da stabilizzante o qualsiasi altro cereale purche’ abbia una sezione conica

    A Google Translation:

    because ‘over the oven do not make a final coat of clay stabilized with hydrated lime and sand and then more and better “arm” the clay with straw which serves as a stabilizer or any other cereal as long as’ having a conical section

  7. hi i think ive come up with a way of stopping major cracks apearing during fireing and cooling. Between the first layer and insulation layer cover the whole oven in chicken wire. i used 1inch holes. i cut it in to strips and sorta stiched it together with the cut ends (note leave a hole where you are going to cut hole for chimney)i then coverd the lot with very thick slip leaving a rough finish for insulation layer to adhere to .I had my oven up to over 300 and no major cracks. yes you do get small crazing cracks but no large ones i reacon when insulation layer goes on ill have no large cracks. In which case as i said befor good masonary paint could help water proof your oven. Failing that, cover it!

  8. hi i have followed your blog and it is great. i have just finished the third layer on mine and have had a few small fires in it to help dry it also this sunshine we have had has helped. BUT is had a bigger fire in it to try some garlic bread and the oven has suffered it has some big cracks appear in it a bit bigger that your winter damage ones and it feels like the third layer is coming away from the second a but cos when i push on the cracks they move quite alot. with your cracks did you rake out the old clay and replace with new or just go over the top. any ideas would be a great help many thanks will try and put photos up when i work out how. ry

  9. Hi Simon – thanks for the blog. My oven is also approaching a year old (having followed your instructions), and has been under tarpaulin since October. I uncovered it recently to find a lot of water damage. I’ve reshaped the dome and filled the cracks, and hopefully will be okay. I was wondering if you have had any further inspiration around how to waterproof the clay? I don’t have permanent roof, so baking on rainy days is currently off the cards! Any ideas welcome.

    • I did exactly the same last week and found rather a substantial amount of water damage on mine this year (it was a bad winter). I’ll be filling in cracks etc myself when we have a good spell of sunshine. I don’t think waterproofing is a viable option. I’m going to build a permanent roof over mine this year. In the winter I will also cover the sides to protect from the near horizontal rain we have had recently! Let me know how you go.


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