Long weekend in Sydney and time to make some progress. First step was to rough out the shape of the oven, igloo-esque seemed to work best. The fire cement ran low and I skimped on this - which has caused some problems. This outline needs to be well cemented-in as the sand mould and working the clay in puts pressure on the sides and a few of the bricks became loose - not so much a problem if your oven is going to be static. A real problem for mobility though!

I built a mould for the door, allowing a lip or the door piece to fit in snugly - this was about 450 wide and 250 high. I weighted this down and then packed the oven space with filler (a few left over Hebel bricks and timber off-cuts). Then the sand mould was created and the flue roughly positioned. This flue is a double-skinned gas flue - it has an stainless interior and galvanised exterior. It’s actually a spacer on to which fits a much longer piece, again something I thought would suit the portability.

Then came the fun bit. My boys helped me mix a 2:1 sand clay mix. We cut the bristles off an old paintbush in order to get some natural fibre into the dry mix and then added a few trowels worth of cement. The whole mix squidged up really quickly when water was sparingly added into a very satisfying (and as it turns out, very throwable, mixture - as my 4 year old discovered).  It took about an hour to get 3 layers on the oven with a constant supply of cunningly fashioned patties. The door area took quite a bit of shaping and cajoling, its fun stuff to work with.

I left out the builder mix called for in the plan I’m following (see part 1). The clay I settled for is called ball clay and comes in 25KG bags costing $30 each - I bought three and have used less than one so far.

A few hours later and the clay started to harden up - it had cracked in two places - expected and easily remedied with more mix. One of these was on the door lip and I decided to lose the option for a tightly fitting door in favour of a more rounded opening (not sure I’m going to need a door as we’ll be cooking mainly pizza). Plus It’s so easy to work with I can aways add this later.

Also, in hindsight I think I should have created a bit more height in the outline, now that the sand has been removed I feel the space looks a bit on the tight side - but we’ll see. More pics to come.


13 Responses to “Part 6 - The oven takes shape.”

  1. Jay says:

    Awesome design, you’ve inspired me to try my own…. Where did you end up finding the clay?

  2. admin says:

    Got it from a pottery supplier in Homebush - its called ball clay and cost $30 per 25KG bag. I bought way too much and have not even used a bag yet, with 2 to return. I’m in Cremorne if that’s any nearer to you and if you want to grab one, let me know.

  3. Jo says:

    Hi

    I love what you have going here.

    Was there any particular reason for building a portable oven other than moving it around your home.

    Why I ask this question is because I am looking at building my own Portable Oven but with more versatility. I would like to take it to Functions, Farmers Markets and all types of social events and just make Pizza Pizza Pizza. This would mean I would have to load it onto a trailer, drive it from one site to another ensuring that I don’t damage it along the way by hitting on speed bumps or pot holes and then off load it at the site. I know there’s a lot to consider when indulging in something like this. That’s why I need your assistance. I would love to build one up from scratch just the way you did.

    Could you possibly help me along the way?
    Also it would be great to get your Email address if it’s not too much trouble. This way it would be easier to comunicate.

    Looking forward to hearing from you

  4. admin says:

    Hi there, because we rent I needed to be able to move it around the property - it weighs something like 200+kilos, so not easy to carry. I also ideally wanted something that would provide the kind of portability that you describe. However, as it stands the design doesn’t really provide that kind of mobility, it’s too heavy and wouldn’t stand being knocked around too much. I’m thinking about some ideas involving a metal structure and more space age-type materials - but that’s a long way off. I think your best bet is to look at a trailer-based structure - like this one… http://slice.seriouseats.com/a.....pizza.html
    The main thing is to get started! My email address is simonbmorgan at gmail - good luck.

  5. Chris says:

    Thanks for the great site. I see that the mixture you used was made of ball clay, sand and cement. The cement that was used, was this regular cement or was is fire cement? Also, the sand, was this builders sand or a different type of sand? This is the best site that I have seen. I have been looking to build my own oven and this site has been the best site I have come across. Thanks

  6. admin says:

    Hi there, yes it was regular cement and builders sand. Let me know how you go with your oven I’d love to feature it on the site. All the best Simon.

  7. [...] should not be more than the weight of 4 or 5 adults. My oven will be a slightly-larger version of this one (but with the chimney OUTSIDE the door); the dome will contain less than 150kg (300 lbs) of [...]

  8. dave says:

    This mix will not really be strong enough for a mobile oven on a trailer. Expect some severe shaking about and slow destruction if you do. The mix will not be fired (clay made permanent) that requires in excess of 573 C The portland cement begins to fail at around 300C you would be better off adding lime which is more refractory. Natural bristles might hold the mix together when laying it initially but will burn out, particularly where they’re on the inner layer. Unfired clay will also shrink substantially so it would be wise to remove the sand former as soon as the dome is self supporting to avoid cracking. I think you could probably do this almost as soon as you’ve finished building the structure. Allow a long time (weeks) for the thing to dry, it will take ages to eliminate the water from the centre. 1 litre water= 100 litres steam (boom, walls split in half.)

  9. admin says:

    Hey Dave thanks for the constructive comments i’m planning version 2 and you certainly have me thinking. Checked out your site and pics- your design looks great. Cheers Simon

  10. dave says:

    The traditional cob oven is a mixture of clay, sand , straw and water mixed to a plastic state. Ovens all over Europe have been made this way for centuries. But they are not permanent and the mix would turn back to mud eventually in extreme weather. A permanent modern solution is to use a castable refractory (essentially firebrick material) reinforced with stainless steel needles. This stuff is expensive, more difficult to handle and hardens quickly, so probably not suitable for the amateur builder

  11. dave says:

    Simon,
    Lots of folk have tried this design with the flue inside the oven, me included. It seems logical and gives you increased floor area, however it is not as good as the traditional design with the flue outside the oven chamber, at the front. Aflue in the oven is going to draw heat away from the chamber too easily. The Romans had a few thousand years to perfect the design I’m sure their ingenuity would have seen lots of variations. The hemisphere with the flue at the front independent of the oven and the door 63% of internal height is about as good as you”lll ever get.

  12. Matt says:

    Great stuff my friend. My daughter is turning one in two months and my wife and I are throwing her a birthday party. I thought a make your own brick oven pizza party was genius until I saw that there were no local businesses that provide such a feature. I am now intent on building one. How much did your oven cost to make? I have seen kits out there for 1250 usd. I am hoping I can build it for much less.

    Regards,

    Matt

  13. admin says:

    Hello Matt - only 9 months too late replying!
    The thing cost around $600 if i remember. The expensive part was the castors. If you can handle a static version (ie dont need the portability) then I reckon you’d be at $300 - and if you could find recycled timber then way less. Did you make yours? Send me a pic. if you did!
    Cheers
    Simon

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