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Post by rodallen on May 31, 2013 22:05:16 GMT
Hi All, I would be really grateful for some advice on my first Cob build. I am pretty new to all this but I have a horrible feeling that the shape of my oven is all wrong (tepee as opposed to igloo). The hearth is a concrete slab that I poured myself, and there is a thick layer of clay, sand and straw, then a layer of sand ontop of which I laid the firebricks. When I made the sand mould I was not careful enough to ensure it was a perfect dome shape and hence the final shape is what you see in the picture. My questions are 1) can I rescue this or should I scrap it and start again - trying to get a perfect dome? 2) Its taking a lot of wood, giving off loads of smoke and not a huge amount of stored heat (went up to 200 Deg C but not much higher). Is this due to the lack of chimney, or the shape? 3) Should I have a go at cutting a chimney and further insulating the outside layer with perlite and cement or something? Cheers Rod Attachments:
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Post by rodallen on May 31, 2013 22:07:40 GMT
heres another picture with some kindling. I got the fire going and flames were lapping round the top of the opening, but I still don't think its an ideal shape and I found it a bit tricky to move the logs around inside. (and the fire kept smoking and going out  ) Attachments:
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Post by spinal on Jun 1, 2013 22:28:16 GMT
Without insulation, you'll lose a lot of heat in trying to heat up all your thermal mass - which currently is the fire bricks, clay/sand and concrete below that.
I would suggest:
- insert an insulating layer under the over, you may be able to raise the oven somehow without scrapping it, depending on access for a forklift or a few wooden stakes and a few friends
- keeping the fire lit will be impacted by two factors (I feel) - a wet oven and not enough airflow. A chimney creates a hot air colum that forces air up (and hence out, and hence into) the oven. That said, plenty of cob ovens have no chimney, so it may be down to ratio - how high is your "dome" inside and the door?
M.
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Post by bookemdanno on Jun 2, 2013 7:04:14 GMT
It'll work regardless of shape, etc but its a case of whether its enough for you.
I think the clay and straw plus sand is a type of underfloor insulation, but its not the best. You'll need several fires to dry ouy your clay before you get a proper idea of performance too. You may have choked your fire too if they smoke a lot and go out. Feed them little and often, with not too large a log. Its hard to get an idea of how big your oven and entrance is from the photo.
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Post by rivergirl on Jun 2, 2013 10:06:22 GMT
As the others have said!! Ovens are slapped up all over the world, all shapes and sizes!! If I was you I would just keep playing with it and finding what works for you and then when the time comes if you found it did not meet your needs you could rebuild! That's the beauty of Cobb. You can always slap another coat on or rebuild and if you can get the clay for free you have not wasted much money. Whatever just remember the golden rule! Have fun!
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Post by cannyfradock on Jun 2, 2013 13:04:32 GMT
I'm another to jump o the bandwagon and say....keep on going with what you have. Trial and error will help light a successful fire (I start a fire at the front of the oven....so the air gets at it, and gradually push it to the center.
Clay ovens are notorious for cracking (normally due to not enough sand being added to a clay that is "pure")...just repair the cracks with more cob as they appear. Once the dome is nice and crisp/cured. you can add a further layer of clay/sand/water and hay to insulate the dome.
I shouldn't worry if your dome isn't exactly in the ball bark figures of the perfect oven (dome height = 50% of the diameter of the oven and the top of the entrance is 63% of dome height)....yours will work fine....stick at it before making any rash decisions to re-build it.
Terry
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Post by rivergirl on Jun 3, 2013 11:30:34 GMT
My first Cob. Sorry these have been posted before but it's quicker for me to repost them. Attachments:
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Post by rivergirl on Jun 3, 2013 11:36:48 GMT
He ( Bert) got belted by a large branch but luckily it was just his nose. So I took it back to where it was pretty stable and gave him a new nose. Attachments:
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Post by rivergirl on Jun 3, 2013 11:40:55 GMT
Unfortunately for Bert this happened just after Christmas as I was about to lob some Christmas decks out!! So he got an extra coat of cob, a new nose and a sex change !! He's now called Bess  The point is , that once you have the confidence the world is your oyster with these builds, the main thing is to have fun! Attachments:
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Post by rodallen on Jun 4, 2013 14:44:31 GMT
Thank you all for your comments and advice. I have to admit I was not happy with the shape and think it really needed to be more igloo shaped so I have scrapped it ready for another attempt . I was thinking about having a go at a brick one - but am a bit nervous about how easy it would be to cut the bricks. |
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Post by rivergirl on Jun 4, 2013 20:47:38 GMT
You will have to ask one of the profeesionals !!! I really enjoyed watching flaming bbqs this week one of his builds was a barrel type pizza oven. It looked a lot easier than the dome type ( especially for amateurs like me !) also wondering about how efficient that mobile brick oven would be fire cemented and insulated.
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Post by cannyfradock on Jun 5, 2013 19:08:51 GMT
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Post by rivergirl on Jun 5, 2013 19:35:13 GMT
Terry thanks for tweaking me !!
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