Phase 2 - Build the Clay Oven

1. Marking out & planning
I wanted to ensure (1) the dome of the oven sat exactly over the arch and (2) that I sited it in the correct position on the sub floor. So I marked it out first with a simple nail-and-string compass.














From the centre nail I first marked out: (i) the 27" diameter oven floor, then (ii) a further 4" of structural clay wall, then (iii) a 4" insulation layer, and finally (iv) a 1" rendered shell.

2. Structural clay over floor
This was my first attempt a mixing the structural clay mix and bedding it together. I followed the book to the letter. Every clay is different and the book helps you adjust your mix to the correct consistency.

The easiest way to mix it is on a tarp with your feet. You want to be working the sand, clay and water into each other. A cement mixer might seem like a good idea here, but its more about pushing the elements together with pressure than mixing and rolling them which will basically tear them apart. There is something in the squeezing and stomping that works the mix into a flexible clay-like mud that is really easy to work with.

One of the tests it mentions to ensure you have the correct consistency is the 'Drop Test'. Basically work a handful of the mix by pushing it into itself over and over until it feels almost plasticine-like. Then drop it from shoulder height on to a hard surface. If is pancakes or crumbles the mix is either too wet or dry respectively. If it plops into a neat cow-pat-like mount then its about right.

So once I was happy with the mix, I just took handfuls of it, worked it on my hands for a short while to get the plasticine-like feel the pushed it into the sub floor (or other clay bits I'd already done) to form the structural clay floor.

3. Lay the fire bricks forming the oven floor
The next step involved laying the fire brick on the (still pliable) clay floor I'd just made and bedding them in around their edge with more of the structural clay mix. This also allowed me to position and cement in the two base bricks for my oven's brick arch entrance.













I left this base to dry out and harden as I knew the next stages would require a solid base. There was some cracking of the clay mix at the corners of the fire brick area, but I just patched this up with more mix.

4. Building the sand form of the oven interior
Now this is where it gets really interesting ! And you have to do this step and the next in the same day - so check the forecast and pick a guaranteed dry day.

Basically you have to build a giant sand castle dome in the shape of your oven's interior. This is done with just damp sharp sand.

IMPORTANT NOTE: You have to use sharp sand for this and the structural clay. Its grain shape locks it together with other grains. Building sand is not suitable as its grain shape is too rounded.

From memory I think the height is about 60-70% the width of the oven. I did wonder if I would need a template for this part, but I managed to get a really good dome just with the hand and eye.













Don't under estimate how much sand is needed for this shape. For my 27" oven I reckon I used about 30-40% of the entire cubic meter/tonne bag.

5. Building the structural clay ovens walls
You need to do this straight after the dome if finished - on the same day. I did these two steps on my own and it took about 9-10 hours in total. I had no idea it would take that long and wish I'd enlisted a mate or two to help.

Basically, you mix up a large amount of the same structural clay mix you built the floor with. Then little by little to work handfuls of mix into each other around the sand form. Do not work the handfuls into the sand dome form. Make the walls about 4" thick and eventually when your hands are numb and your back aching your have a perfect, beautiful clay dome - and its worth all that work!













6. Cut out the door and empty the dome
I left the clay dome for about a day and a half before cutting the door out. I wanted it to settle and harden a little but not to the point where it would become brittle.

According to Kiko Denzer's book Building Your own Earth Oven the ideal height of the door is about 63% of the oven's interior height. So with my calculations in my head, and a large knife I cut the door shape, with some trepidation I can tell you ! But that all went well so bit-by-bit I dug out the door shape to reveal the sand done interior.









Once this was done, and I could see the sand dome inside the clay oven wall shell, I dug into the sand a little around the door edges to see how the clay interior felt. Feeling solid enough I proceeded with emptying the oven of all the sand inside. Again, I felt a little nervous after all the hours I'd put in, but nevertheless confident that it would hold.










... and it did. Fantastic!

So I let it sit for a few hours, then lit a small fire inside to help dry it out.

And that is basically it - Everything from here on is optional - the insulation, chimney, brick arch, exterior render. When I get a mo, I'll write these up as a Phase 3.

What I should have done at this point, once the oven was fully dried out, was light a full size fire inside to ensure it got to the temperatures I needed (i.e about 500+ Celsius). But my judgment was clouded by my achievements and I wanted to finish every off and get it just right. So after a week or so I move on the the chimney and brick arch.