To make a cob oven dome, you first need to prepare the wet sand mould that you put the cob over.  The basic principle is you create the sand mound, followed by a layer of wet newspaper, followed by packing your cob over it, building it up cob layer after layer, until it’s finished.  You can then cut a door, remove the sand – and bob’s your uncle – a cob oven is formed.   That’s kind of it.  But lets start with the prep.

Create the wet sand dome, damp newspaper and first layer of cob on the same day.  

We found sand at a local bush area, and filled up buckets of the stuff into our car boot.  We then brought it back to our oven site, popped it on a tarp, slightly wet it until it was like the type of wet sand you have when you build a sandcastle.  Then you just build your mould.

The size and shape of your sand mould will be exactly the interior size of your oven of course.     Remember big isn’t necessarily best – unless you have massive dinner parties every weekend,  we think smaller is more functional.  It’s likely to be used more often and is quicker to heat.  It will also hold the heat longer.

The theory of the interior cob oven is that your first 10-20cm of your oven inside should be straight up, then shaped into a dome.  We kept it as best we could to the avocado shape that is recommended as the ideal shape for fire retention.   The fire/heat would ideally come up the deep round part at the rear then coming up the back wall and ceiling and then sloping down to the exit/chimney or door chamber.

The circumference of your dome is determined in part by your floor.  Remember you will be building thick layers of cob which need to be supported by the base, so the dome is quite a lot smaller in circumference than your floor.  We used string – held in the middle by one person, while the end of it (with pencil or chalk, created a rough perfect circle to guide size.    Start packing wet sand. (remember, straight edges for about 20cm, then gentle avocado shape.)

The height is important.  Try to get it about 75% the size of your width.     Off you go – and build your sandcastle.

You can see from our photos we didn’t quite get the avocado shape, and we didn’t quite get the straight up 10cm part.  Point being here it didn’t matter – so don’t be too hard on yourself!.  Our pizza’s now cook within 2 minutes of putting them in the oven.  So it’s working as it should.

The wet newspaper layer.

Once the sand mould is done it’s time to put plastic & wet newspaper on.  This is to separate the cob from the sand.  It will be easy to remove the sand and reveal a smooth inner cob wall once done.  You can see we just put black plastic followed by wet newspaper.  Then we started straight into the first layer of cob.   That’s the next step!