Part 4: Earth oven, finished!

Want to see it in action or try cooking something in it? Join us at Saffron Acres for a relatively low key Halloween-Harvest type fun day on Saturday the 18th of October from about 12 noon onwards. More details about the event at the end of the post, however, let’s finish the building first…

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Previously, on LESSBIG…

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The base was complete, starting to add whitewash and now we were ready to tackle the actual oven.

(See Part 1 here)
(See Part 2 here)
(See Part 3 here)
(See Part 3.5 here)

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A sand dome provides the inner support to build the dome of the oven around. But wait! That’s a bit lumpy isn’t it?

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Eagle eyed readers will notice some additional items have been added to our pile. We were a bit short of sand so some bricks and logs were added. As long as it’s solid enough to support the dome, in theory that’s fine. HOWEVER! Sand is dirt cheap and you can reuse it for all sorts of things afterwards. One thing I would do next time is make sure I had enough, possibly even more than I needed… for reasons that will become hilariously obvious to you soon, dear reader!

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Wet newspaper layer over the top to help indicate where the edge of the dome will be when we come to take the sand out.

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First layer, the dense layer of clay with barely any woodchip added. This was about 2-3 inches thick and for a dome this size, we probably needed 1 full heaped wheelbarrow of earth – remember, there’s no woodchip or straw to help bulk it out.

 

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Cutting the entrance with a pointed trowel. About 12 inches wide.

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And 10 inches tall. After experimentation we may need to open this up more, add a chimney. Depends on the airflow really.

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After the first layer and cutting the door, we start with the second layer. I crosshatched the first layer with a trowel because… it seemed like a good idea. Plasterers do it, don’t they?

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Finishing off the second layer. We left it to dry between layers while we had lunch, so it was possible to come back and fill in a few cracks before the second layer went on.

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Left a bit of a notch here between the two layers, potentially to help hold some kind of door.

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Adding whitewash to the dome and the base. While it won’t seal up massive cracks, it does help a great deal to get a smooth surface especially if it’s not too watery – although most sources suggest many thin coats (as many as 4+) of whitewash are better than one thick coat. As we saw earlier with wood, the difference between more or less porous surfaces makes a big difference.

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Wow that’s bright! (also camera issues as noted before)

 

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And this is where we hit a problem. The sand was no problem to get out, the smaller bricks were okay…

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…but the bigger bricks and logs were tightly wedged in there! After about 20 minutes of fiddling around, some of which was very tense and produced some disturbing bulges and cracks in the dome, I got out as much as I could. The solution seemed to be to burn the remaining bits of wood out with a test fire once the dome dried out. Arg!

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Fire in the hole! Even with the ashes; the oven thermometer just inside the opening pointing at about 200c here (shortly before I realised the thermometer was melting at the back… it’s a learning experience, alright?)

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After some burning and (more effective) chiseling, I finally freed up the two big chunks of log. Just use sand next time kids! (or at least smaller bits of log that will fit through the opening!)

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I was pulling bricks out as well, and here’s that thermal mass in action, they had absorbed a lot of heat! (note to self, next project: sauna)

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Thanks to Rob at the allotments who chainsawed up this log into a rough door for us. The dome is brown again as I put on a final layer of earth to seal up more cracks and generally add mass. It was mainly from the mini demo-dome we’d made earlier, plus I added several trowels of lime to the raw mix. Hopefully this should help stabilize it as well as the limewash which will go back on.

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First go at some basic cooking, though as the third layer was still drying out it was not very effective at all.

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Some slightly warm smoky corn on the cob though, not awful! And yes, the oven thermometer definitely broke. (thanks, Heston Blumenthal…) I am looking at buying an infrared one instead, there are lots of cheap ones on t’internet that can measure 300c+ or higher. Not much point aiming it at an open fire of course, even a candle can apparently be 1000c.

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Left it to dry for another couple of days, quickly popped in once to finish off the whitewash, left that to dry, then it was the real moment of truth. As you can tell by this especially flattering photo, it seemed to be working, and I seemed to be pretty happy about it!

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My crappy dough making skills aside, you can tell in this photo I was rather excitable as I’d already taken a bite out of the one (dumpling? scone? general doughy lump?) before I thought to take a picture.

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A shop bought pizza topped with tomatoes, peppers and chilli from the polytunnel. How do you get a circular pizza on a rectangular tray? Who said tessellation would never come in useful in real life? Kids – maths is cool!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Pizza #1 going in…

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Took about 4-5 minutes! The chillies in particular were excellent and a good match for the woody-smoky flavour. It was probably too hot when I put the pizza in (there were still flames) but I’d rather over-egg it on the first try. Still learning how it works really, all ovens are likely to be different, also depending on the type of fuel you’re putting in.

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Some more of my wonky dough complete with Saffron Acres’ own strawberry jam. Left this in for longer, seemed to do okay but perhaps was a bit dense and not-very-well-kneaded to rise. Even so it was happily shared among anyone who happened to be in the general vicinity!

 What have we learned?

– Earth is quite literally, dirt cheap, providing it’s got a good amount of clay in (say from 25-75%). This oven cost nothing except time, a bit of sand and a sack of hydralime (of which we only used maybe a quarter at most).

Cordwood (the base) is also dirt cheap providing you have access to logs you aren’t going to be using for anything else. We could have been pickier about using uniformly shaped pieces, and also pieces without bark on. Remember the core is also full of some odd bits of rubble. The sheer weight of the whole thing is probably the main thing holding it together.

– Later we drilled a small (ie finger-width) hole in the rear to help the fire get started. It’s partly impatience but I’ve found myself fanning the fire quite a bit to get it going and as hot as possible. It’s not too much hard work, but leading to another observation…

– Overall this dome is on the small side, compared to some others out there on t’internet. This obviously affects how much you can cook in it at one time, as well as the amount of airflow through the door.

– It’s hard to be scientific about it, but wood chip in place of straw for a cob mix seems to perform similarly (structurally and thermally). The longer, thinner fibers are probably more consistent and easy to mix than lumpy wood chip.

– The glass bottle layer seems logical but I don’t have anything to compare it to. Firebricks for the base also might have been beneficial but the concrete pavers we used seem fine. (Though will have to see if they breakdown over time)

– Digging, sifting and mixing was probably 75% of the whole effort. For anything much larger, some mechanical help would be recommended. Of course you may not have this much lying around, or don’t fancy digging a pit in your garden which introduces the issue of transport costs.

– Some of the other side benefits of earth buildings can be seen: it’s relatively non-toxic (though too much dust can be a thing, or splashing some limewash in your eye) and is a good insulator. It’s almost completely fireproof.

Come and cook!

We will be having a open day of cooking Saturday the 18th of October from about 12 noon onwards. The oven will be lit and you’re welcome to bring anything along you want to try out. There’s extra veg around for pizza toppings, corn on the cob, salad bits. All welcome, limited parking on site if you are coming by car. Bring a bottle. (Jesus, I hope the weathers okay…)

For those of you who don’t know where Saffron Acres is, it is fairly central, on Copinger Road, just off Saffron Road. Near the Aylestone Leisure Centre.

Email me at : rfletcher@dmu.ac.uk for more info

Hope to see you there!

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