Cracks in drying cob oven

Hi, we’ve built a cob oven and looks great on outside but inside is cracked.  It isn’t completely dry yet, cleared sand just under 2 weeks ago.  Inner layer we didn’t use straw but outer we did.  We keep filling the crack but keeps appearing.  Will it do this until dry?  Should we just keep filling the cracks.  Is this a lost cause?

Keep on plastering a wet clay slip over it and dont worry these ovens are maintained constantly it never ends its not a Zanussi

Andy Parker wrote:Keep on plastering a wet clay slip over it and dont worry these ovens are maintained constantly it never ends its not a Zanussi

Thanks Andy, we have been filling as it dries and the cracks are less and less.  It’s looking really good now and we’ve done a few small fires to help drying.  Love working with cob and as our first go you just get a bit nervous if it’s all worked or not.

Here I am adding tiles to the base, it’s taking shape :)

Beautiful oven!

Make notes on what your mix was, and remember for future cob projects, that too much clay tends to shrink and crack on drying (but too much sand tends to crumble, so you have to keep adjusting till you find the perfect mix).

Rebecca Norman wrote:Beautiful oven!

Make notes on what your mix was, and remember for future cob projects, that too much clay tends to shrink and crack on drying (but too much sand tends to crumble, so you have to keep adjusting till you find the perfect mix).

Thanks Rebecca, we did work out there wasn’t enough sand in our first layer.  Luckily the other layers were a better mix so the cracking hasn’t gone all the way through and we filled in the inner layer with a better mix.  Good learning curve though.