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Clay Oven on Verandah

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  • aussiepizzaman
    replied
    Re: Clay Oven on Verandah

    hi Mick,
    I was going to build something like your oven until i came across this site.
    nice job so far and will be interesting to see if no further cracks appear.
    all said and done each build is different , its the end result that we are after, an oven that can cook pizza and slow roast meals for our family and friends to enjoy.
    good luck on the finish and enjoy your first pizza when you get to that stage.

    regards Gary

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  • BackyardPermaculture
    replied
    Re: Clay Oven on Verandah

    OK, thanks, I'll keep going with smaller fires then.

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  • david s
    replied
    Re: Clay Oven on Verandah

    Handbuilding clays that have a high proportion of aggregate seem to dry slower than those that have a low proportion. It's hard to say how long to wait, but I've found that thick sculptural work needs at least three weeks slow drying before attempting firing. The outside surface may appear dry, but the inside will still contain moisture. Most of my accidents from "blowing" have occurred at around 300 C You might be safe to try to avoid higher temps until you've fired it about 6 times. The smokey problem always occurs with a new, moist oven and it will just keep improving the more you use it. Try to keep the oven warm with heat beads which will provide a safer gentler heat until you're sure it's completely dry.

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  • BackyardPermaculture
    replied
    Re: Clay Oven on Verandah

    OK, cool, but it's been 15 days and I've had small fires in there most of those days. Is that too soon? If so, how long? Thanks for the good advice, cheers, Mick.

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  • david s
    replied
    Re: Clay Oven on Verandah

    Five days between finishing the cob and your first fire is way too quick. Rushed drying leads to warping and cracking in pottery and an oven is way thicker and will take longer. Can't emphasize enough the importance of taking it slow. I know it is hard because it is so exciting, but I'd hate to hear yo report that your oven walls have cracked and split from the centre. Slow down you move too fast, gotta make the ....

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  • BackyardPermaculture
    replied
    Oven now insulated

    My cob oven is getting a lot closer to being finished - I've made most of the enclosure and completed the insulation.

    The enclosure is fairly standard - metal framing with FC sheeting.

    Insulation is 50mm thick rockwool, and loose vermiculite. This rockwool insulates really effectively; I've got one layer over everything and a second layer on top. I then poured loose vermiculite to fill up the sides.

    I ran a much bigger fire last night; lots of water came out, which meant the top of the rockwool got hot and steamy. We still managed to cook chicken legs and steak over corn cobs - have never had such delicious corn!

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  • david s
    replied
    Re: Clay Oven on Verandah

    The heat beads are also great because they don't flame up and release their energy quickly. When the oven is new and contains moisture it is a bitch to fire. The fire is hard to keep going. Try a gas burner.

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  • Archena
    replied
    Re: Clay Oven on Verandah

    Low and prolonged: build a small fire on two long sticks. As they are consumed move the sticks a little further in. This is how people with limited firewood cook in the Third World. If you need to extend it, add a third long stick before the others are consumed.

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  • BackyardPermaculture
    replied
    Re: Clay Oven on Verandah

    Thanks David - not so easy to keep the fire long but prolonged, but I'll give it a go.

    Unfortunately the oven gets no direct sun on it at this time of year, so I will probably have to continue trying to heat it. I think I'll go back to the plan of using heat beads or some other commercial fuel to try to get a consistent small fire.

    There's rain coming soon, apparently, so I need to be careful not to let it get drenched too.

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  • david s
    replied
    Re: Clay Oven on Verandah

    With the kind of thickness you have in the walls the moisture is hard to eliminate from the middle.If the temp gets up to around 300 C expect your wall to start splitting from the middle. You might think that they're dry but they won't be. Don't be in a hurry and let nature do the a lot of the job for you. Try to keep the fire really low but prolonged. You will have added maybe 50L of water. How long do you think it would take to boil a 50 L drum dry? Use sun and wind to your advantage.

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  • BackyardPermaculture
    replied
    Second Fire

    I lit another fire in the clay oven last night. Got it a bit too hot one one side - lots of steam came off that side, and one crack appeared when it cooled down.

    Easy to fill in the crack with the sand/clay slurry, but it shows how much moisture is still in there and how careful you need to be in getting it out.

    The oven was drawing really well; much easier to light the fire this time and very little smoke (which was almost all drawn up the flue). The dome is drying out to an almost-white colour now.

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  • Archena
    replied
    Re: Clay Oven on Verandah

    Great! Congrats!

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  • BackyardPermaculture
    replied
    First Fire

    Just ran my first fire in it tonight.

    I ended up getting it pretty hot - dome was feeling quite hot on the outside; definitely pushed a bit more moisture out. No cracks so far, which is encouraging.

    Really happy with the design - most of the smoke drawing strongly up the short bit of flue pipe I had on it.

    Also really happy with the performance of the AAC layer (Hebel). The blocks cost me $64 at Bunnings and took about 30 minutes to lay on some adhesive. Much easier than pouring a vermicrete layer.

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  • BackyardPermaculture
    replied
    Re: Clay Oven on Verandah

    Archena,

    Thanks for that. I was actually still trying to decide between an igloo with acrylic render and an enclosure. Sounds like enclosure it is!

    Leave a comment:


  • Archena
    replied
    Re: Clay Oven on Verandah

    If you are going to put anything on the dome other than lime you MUST have an enclosure. I'm pretty sure you were planning on one but it is vital if there is anything on the dome. Anything that can potentially seal moisture in or inhibit evaporation will destroy the cob. Be sure the exterior is dry before you add the insulation.

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