More cob oven details and photos | The Year of Mud: Building a cob house
They’ve posted some more pictures of the oven. Including some showing large cracks in the outer insulation layer which may be due to the inner layer not being dryer before the outer insulation layer was put on.
I had similar cracks show up in the ones I have built but I had figured it was due to the inside lining being brick rather than cob. I remember one I built a couple of years ago that I tried to seal with repeated coverings and filling in of the cracks with cob and clay and creek sand but they kept coming back and getting worse. Looking at the pictures of this one it seems that some of the cracks start at the door arch which is done in brick, so I’m wondering if the same thing is happening with it.
The next one I build (and it will hopefully be soon) is going to be made completely of cob other than the firebrick floor. I’m thinking of floating the walls of the inside dome on a thin layer of sand or ash to keep it from bonding with the floor brick, which will hopefully keep the expansion and contraction of the dissimilar materials from cracking the cob walls. Also planning on using a loose ash insulation layer 3 to 4 inches thick between the inside heat dome and the outside insulation dome, again to try to minimize cracking.
Technoprimitive 3 
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