Monday, August 30, 2010

Hairy oven

I got the front part of the oven covered in the first layer of cob today. Bits of straw are sticking out all over the place. It looks hairy.

Mixing the cob is the nasty part. Slinging around the sand and clay, then spending more than an hour (yes, that's how long it takes when your helpers get busy with other things) mixing the stuff together with water and straw. It would probably be a fifteen minute job with a helper or two, but the ergonomics just don't work solo. I'll count it as my cross-training for today. My core workout plus aerobics.

Weather was nasty and blowy today. Cool and fall-like, threatening rain on and off, lots of wind. I rigged a tarp over the oven so I could continue working, and ultimately to allow it to dry a bit more easily.

The cob went on really easily and much faster than the first layer. It's a bit softer and wetter, so much more forgiving in the hands, and there's no worry about pushing the wrong way and collapsing the sand. The thermal layer had firmed up enough that one can push freely into it.

You can see the two layers where the doorway is. The inner one is a bit darker because it's dried out a bit. The wall of the oven is now 6" (15 cm) thick. We'll be adding another 3-4" by the time we're done. If you compare this photo to that of the sand dome in my earlier post, you'll see how much it's grown already. It's mind-boggling how much mass is involved in the oven. There were three loads of rocks, each a couple of hundred pounds, plus four wheelbarrows full of mortar. Then at least eight almost-too-heavy-to-push wheelbarrows full of drainage material inside the ring of rocks. So far for the walls: two garbage cans full of sand, a 50 pounds or so of clay, and water to wet it all. And we're only about half way done building the walls of the oven. I guess they don't call it a thermal mass oven for nothing!

I also enlarged the doorway today. It's now almost the width of the four firebricks that form the apron, to allow passage of our family's standard 14" pizza. Which is most important.

I have been looking at oven tools. We'll need a coal rake, a scuffle and a peel. The coal rake sweeps the coals of the fire out the door into a metal bucket. The scuffle is a bunch of wet rags attached by a swivel pin to a long pole: it's used for cleaning the oven floor of ashes prior to starting to bake. And a peel is like a giant long-handled spatula, used to insert and remove whatever you're baking from the inside of the hot oven. My resident blacksmith/carpenter should be able to make these for us.

Earth ovens take many weeks to dry out. You can speed drying by firing them, but then they're prone to cracking. Which is pretty much mostly a cosmetic issue, and can be fixed with more cob. I'm hoping we'll get a sunny warm September. Then maybe in October we can fire it up.

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