The base is what you put your cob oven on top of. This can be anything from bricks to a flat top truck (yes mobile wood-fired ovens do exist!). We decided to make ours out of found materials and so made it quite rustic using boulders of sandstone to build a dry wall and fill with urbanite.
What is a stone dry wall. Kind of exactly what it says – a wall made out of stone with no mortar. Big rocks or boulders are gently and carefully placed on top of each other and arranged in such a way that slowly and steadily a strong wall is built. It’s a very very old method and conjures up old county lanes. So we did that but round. The hollow part in the middle we filled with urbanite.
Building the stone wall to a certain dimension will of course determine how big your oven will end up being. We read in quite a few places during our research the best shape is something like an avocado – not perfectly round. The slightly smaller end is towards the door and the oven is more oval than round. Having said all that ours ended up being pretty near round and cooks beautifully. As we said – we aren’t the experts here, so you’d be advised to read up a bit more about this if you are after perfection. If you are after ‘pretty good’ – then somewhere between round and oval is a good place to start.
What is urbanite. It’s broken concrete, sand, junk essentially that is solid and fills it up. If you look around you’ll get the feel for the height. Probably about hip height. Remember that on top of it you will put layer of cob, glass bottles, more cob. Then your firebricks. The firebricks are the floor of you oven – so around bench top height is where you want to end up. Work back from that.
So – once you’ve built your stone wall to your preferred height and you’ve filled it up with stuff you then need to fill up the gaps with sand. Lots of sand.
Once it’s all filled up, you flatten out your sand to get ready to put your first cob layer on. That’s in the next step.
