Next Step: Insulating

The insulating layer for the oven should be made up of clay and earth and sand like the thermal layer, but most importantly it needs to have a lot of straw or light-weight filler material mixed in within it.

 

You want the material to be light and airy, to keep in the heat that has been soaked up into the thermal layer below it. 

So I got a bunch of straw from my brother who has a couple of chickens. 

I had dried grass that I had saved from the first time we built the oven. (What kind of a nutcase saves bags of dried grass? Me. You never know when you might need it in this Craft.)

To shred it up very fine I figured out that a weed-whacker and garbage can would work well. 

It does work well, but wear a mask! 

Then we combined the dry mix with water and mixed it all up to produce a really good clay slip. Nice and creamy and muddy. 

 

And then, in the wheelbarrow it goes, with lots of straw. The idea is to wet the material just enough so it sticks together and not to pack it too tightly in your hands - you want insulating pockets of air in there. 

    

Slap it on the thermal layer about 3" all around. We used little 3" sticks stuck into the lower layer to show us how thick to go. A couple of hours - it goes more quickly than the first thermal layer because you don't have to pack it so tightly - and it's done. (Not many photos because muddy hands and cameras don't go well together.)

Time to let it dry slowly, and then take it for a test drive.