I had been recently informed about Perlite, a naturally occurring volcanic glass that has excellent insulation properties.
We mixed it in a thick clay slip to add to the existing cob oven, which was losing more heat through its top than I wanted.
It mixed up very easily and was applied just as easily, holding the shape we wanted. As you can see, it is easily sculpted, too!
The first bake took about as long as before applying the perlite/clay topping since it was still not fully dry.
But the next bakes used about half the wood and took just over half the time to heat the oven to temperature. Each baking session included a first round of bread and a casserole, then a round of granola, Anicca's Chocolate Cake, and carob chip cookies. Total baking time was only an hour and everything was baked to perfection.
Next time, we'll put our yogurt inside over night to take advantage of the residual heat....