It might be so disappointing to see the walls of your cob oven crack. Therefore, it is always imperative to prevent such event from happening. The main reason as to why the walls of a cob oven may crack is the presence of water in the oven. You should ensure that the oven has completely dried up before the initial firing. This is because the water on the inside walls of the cob oven will turn into steam and then try to escape. This will form cracks on the walls and may take away the beauty of the oven or cause the entire oven to collapse if the cracks are intense.
Additionally, the cob oven should not be rained on as the water will turn into steam once the oven is fired. Therefore, in order to prevent your cob oven from cracking, build a rain cover over the whole oven to prevent water from touching its surface. Also, before the initial fire is lit, ensure that the oven has completely dried up.