Hi I'm Dan, i live in the UK and have just build my 1st Clay/Cob/Hybrid oven. After a lot of looking around online during Lockdown i decided i needed a good project to keep my busy and sane!
I decided on a clay thermal mass dome as i live on very heavy and very pure clay soil only 18" down, followed by some refractory silicate blanket and then topped up with a bit of vermi-crete (found in my dads shed!) and straw cob.
My next project for a friend i am planning on more sustainable resources, and using sheeps wool , possibly in a light clay slip as the insulation.
Hey Dan, Welcome to the Forum! Traditionally, some Quebecois Ovens were built using pure clay. Would love to see a photo of your project if you have any.
Using pure clay will work to some extent, but you will have to keep patching the cracks. Cob is much stronger and it holds more heat, as it is 75% sand the density (thermal mass) of the sand stores more heat than clay, and it reduces cracking. Experimentation is fun, but I highly recommend building an oven following proven methods first - A great book is Build Your Own Earth Oven by Kiko Denzer.
I made a post on how to mix oven materials here if you want to follow proven methods. If you have any questions feel free to post them on the blog. Oven proportions are the other thing I would stick to the proven methods - The door height should be 63% of the inside Dome height, this will ensure you get a good draft. I hope you consider documenting and sharing your project with us here!
Thanks for the intro.