Courtesy of Helen Atkinson in Baltimore Now for something a little different. Something a little fun. Not that Helen’s cob oven is particularly ‘little’. Au contraire, this wonderful project is quite the cob oven piazza:) Ah, there’s so much you can do when you learn the art of cob and earth plaster. Your imagination is the only limit. As soon as Helen joined The Mud Home Facebook group last year, she began sharing her oven progress. What I loved about her posts was how she clearly enjoyed experimenting. This is Helen’s third cob oven now, and each time they get better and better. There's a lot of very good information coming here, no matter how much you've researched cob ovens, so do read it all. Why Three Ovens? “The first one had way too many deep cracks in it,” explained Helen, “So I tore it down a few days after the build and rebuilt. The second one included a four-inch layer of insulation and was great. We had some lovely pizza parties, but when I forgot to put the tarp on and it rained, there was some definite erosion. Now the third iteration has a whole new (flat) floor under it and roof.” Do You Need A Roof? A roof over a cob oven is pretty much always recommended, unless perhaps you are in the desert. Rain will indeed erode that cob dome. But I love how Helen kept improving her design like this. Cob ovens routinely fail, for many reasons. I know when people experiment and tinker and redesign, they have learned deeply what works and what doesn’t. Not being one to miss an opportunity like that, I asked Helen for all her tips. This oven is very well done. Many thanks to Helen for this very detailed explanation. It will be useful for anyone wanting to give this a go. How Helen Made Her Cob Oven 1. First she built the foundation out of stacked prefab stones from the hardware store. “The ones that are used to build round fire pits,” says Helen. 2. Next she filled the empty round base (which was almost hip height) with ‘urbanite’ from a roadworks nearby. "We fetched it in wheelbarrows," said Helen. "And then added sand to fill the tiny gaps. After that I put a border around the base made of large and small river rock collected from a park nearby.” 3. It’s advisable to add a decent insulation layer underneath the actual oven. This helps the oven heat up fast (otherwise all the heat is sucked down into the base). A good way to do this is with a layer of recycled glass bottles. Helen embedded the bottles in sand and then about 3-4 inches (10 cm) of cob. 4. The oven base is formed out of fire bricks. “I put a 3-4 inch layer of cob on top of the insulation layer, so that the outer edges would meet up with the oven sides and be like a chocolate covered peanut. Next I put some sand down in which to arrange the fire bricks, laid the fire bricks carefully in the centre in rows and a large flat stone to stick out the front so I have a lip to drag the ashes out into a bucket,” says Helen. 5. The dome of the oven is made from cob. Here’s how she made the cob dome: i) Helen shaped a sand pile into a round mound on top of the firebrick base (16 inches high). ii) She covered the sand pile with wet newspaper (makes it easier to remove the sand at the end). iii) She covered the sand mound in 4 inches of cob. This is the layer that is built to take the heat. Her tip here was to press the cob down and around the sand dome in a spiral (rather than patting it against the sand dome itself, which moves the sand around in the middle. iv) Once that was completely dry, she carefully dug out the sand, leaving the clean oven floor (firebricks) with a cob dome on it (Sigi Koko has a great YouTube video on how to do this step). 6. Next she added a 3-4 inch layer of insulating mud onto her cob dome, that included dry hamster bedding. The hamster bedding is supposed to incinerate and create pockets of air. “A friend gave me an old cast iron stove door, and I built a doorway out of fire brick with a chimney made from an old piece of ceramic pipe, and used a stiff mud plaster to cover it all and hold the chimney in place,” Helen said. 7. Now that the oven structure was built, Helen plastered the whole lot with an earthen plaster she made with deer poop added (for the record: you don’t have to plaster the base of the oven, it was an aesthetic touch). 8. Next she decorated her new oven in beautiful mosaics and sculptures. Once it had completely dried she coated it an a whopping 7 coats of linseed oil. “I think this is what really saved me,” she said. “Even though I had built the shelter to cover the oven there is enough sideways wind and rain to wash the sides away without the oil.” Take note folks! So there you have it. How to make a very good cob oven that heats up fast and doesn’t collapse in the first rain of the year. Of course I have to ask what will come next. Perhaps an entire cob oven complex with cob benches and picnic tables and… Just joking Helen:) The Top 3 Reasons Cob Ovens ‘Fail’
As I said, cob ovens do misfire quite often. That’s not really the end of the world if you’d like to just have a go. Ultimately we all learn from our mistakes a lot faster than we do from online commentators like me:) But for the record, here are the most common pitfalls: 1. The oven isn’t adequately protected from the weather. You really need it well covered, preferably by a roof. And if you’re in a rainy climate, some linseed oil won’t go amiss either. 2. Not enough air flow, so the fire struggles to get going. For the best suction, you want an entry point for air (small flue or tube, or open oven door), and an exit point for smoke (chimney or flue). 3. No insulation. This means it takes an age for your cob oven to heat up. If you’re baking pizzas all day this may not be such a drama. But if you want to get cooking fast, then insulate. Related links: The free earth plaster course: http://www.themudhome.com/earthplaster-sign-up.html Cob vs earth plaster, what's the difference? http://www.themudhome.com/mudbuilding/earthen-plaster-and-cob-whats-the-difference Do you enjoy The Mud Home? If you find these articles inspiring or useful please consider joining us on Patreon. Your support pays for the running of this website, my virtual help, and my sustenance. A big thank you to all The Mud Sustainers, and everyone chipping in and keeping these posts and articles coming.
3 Comments
Emma
30/4/2021 02:54:40 pm
Such a gorgeous end result! Really makes me want to give it a go and get cooking. I'd love to hear how the finished result works. I had the pleasure of eating cob fired pizza in Belize that cooked really really fast. I wonder what Helen prepares in this oven and how long it takes?
Reply
Helen
30/4/2021 05:29:14 pm
Thanks Emma. The oven works really well. We’ve measured temps up to 800 degrees. I’ve only done pizza so far and had to stop that due to covid. But I’m starting it up again this weekend. I love the fire part so I tend to start it earlier than necessary but it probably takes at least two hours to fully heat. I leave the hot coals round the edges for the pizza part and add wood if it cools off. I’m still experimenting with the dough and I’ll get around to baking more this summer (with the coals out and a door to block off the chimney). I like it best when one of my grown kids takes over the cooking.
Reply
Emma
30/4/2021 08:12:55 pm
I know what you mean with the fire part too, I think I'd enjoy that part. I have a good pizza dough recipe that works well in a regular oven. It has yeast though, are you sour doughing? Do keep us posted on what cooks well in the oven. I'm fascinated. Leave a Reply. |
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