The second layer of the clay oven is an insulating layer. It consists of the same clay/sand mix described previously but with the addition of an insulating material. I decided on straw. This mixture is known as a “cob” mix and has been used in building and insulating for thousands of years.
Here is what the mix looks like with the straw sprinkled over the top.
It then gets well mixed into the clay/sand.
The cob mix is then made into bricks and built up around and around the inner layer. I have made this layer also about 60-70mm. As you can see from this image, the inner core has hardened to a strong smooth finish.
The layer is then slowly built up, pushing down, pushing in and then smoothing after every revolution.
This is a pretty rough layer with straw stalks sticking out all over the place. This is not really a problem because a final finishing layer of about 30mm will seal off everything nicely.
I am busy firing the oven again tonight and the insulating layer appears to be drying and hardening exactly according to plan. Steam is rising off of the wet clay. The “63%” door opening is working like a charm.
I should have the insulating layer hardened enough to complete the finishing layer before the end of the week. Now I just need to make the door and possibly varnish and seal the timber stand and we’ll be eating bread and pizza made in the oven by the weekend.
Enough for now.