Sunday, July 27, 2008

Insulation Layer

I was eager to get going now that I finally was in possession of the cement.
The oven can be thought of as a brick chamber surrounded by a thick layer of high temperature concrete and a blanket of lightweight insulation.
The insulation consists primarily of vermiculite. Vermiculite is a mineral that when heated up expands into puffy worm like (thus the "verm-") particles, sort of like rice krispies. It is also used as a soil additive to loosen up clay soils or retain water in sandy ones. Once the oven is complete loose vermiculite is poured over the oven as a loose fill insulation. Beneath the oven it has to adhere to itself and the bottom of the oven and so is mixed with a bit of portland cement (the primary binder in concrete) and poured onto the forms that carrie helped me make last time i did any real work on the oven.
Before the vermiculite is poured 6x6 mesh is put down with some of the struts bent up. The mesh will help to hold the vermiculite layer up. The bent struts will hold fast into the concrete layer above it.
Once the mesh is in place the vermiculite cement layer is poured wall to wall to a depth of about 3 inches.
Sarah (my sister) regards the pour of the first batch of vermiculite as we both realize that this is going to take a while.

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