Thermal Layer

The first layer, or thermal layer, is a mix of mostly sand. A small amount of clay and water were added just to get it to hold together. The less clay, the less the shrinkage between firings. But enough clay has to be there to hold it all together and give it a little give. Too little clay and the roof caves in. We were pretty nervous. This was the "make i t or do-it-all-over-again" stage.



The mix was not easy to work with, but if we smashed it down and molded it, it worked just fine.






It was fast work, once we got how to squish it together and measure it with our hands as we went. Sadly, we ran out of mix just before we got to the top and had to make a sand run so we could make more...



But we got it done before the sun set.



We then got a 2x4 and whacked the sides of the oven to set the sand into the clay and firm the whole thing up. We also rocked the board back and forth across the surface between beatings. It started to almost shine.


The book says that we can cut the door out at this point. But we were still nervous about the mixture and decided to let it dry a bit before cutting it out.