Most people who have a brick or clay oven love to use them, particularly during warm months when cooking indoors becomes difficult because of the heat.

With this plan, which is scalable, the trickiest part to the entire process is the time it takes to dry.

Fire Bricks

I picked up some fire and laid them out to give me an idea of the size of the floor area. It helped me work out if I would have enough room for all the layers.

Bottom Insulation

After a bit more bricklaying. I decided to use the wine bottle insulation method. I had been diligently drinking lots of beer and wine for months. I think I had about 3 times as many bottles as I needed when I actually built it. The gaps in the bottles (leaving room for them to expand under heat) are filled with a clay slip and saw dust used for pet bedding which I picked up from a pet warehouse place. The clay slip is clay that I had kept from digging the foundations, not much but enough for the base. I soaked the clay in water over night and mixed to a double cream type consistency with a plaster mixing attachment I had for my drill.

Oven Floor

You are meant to (so I read) put a layer of build soil mix under the fire bricks to give yourself a firm level base to put your fire bricks on. No cement or clay needed. Just work out the best fitting bricks on the floor first. Choosing the best fitting ones for the middle where your bread or pizza will go.

Clay

Now to get a lot more clay. I found this a bit of a problem as we only have a small garden and live up in the hills on gritstone. So not a lot of clay beneath our feet, or not very pure stuff at least. After scratching of my head the only place I could think of was my mum and dads house down in the Cheshire planes. Not very local but I knew it would be good as there house is made out of Cheshire brick. Which was probably made with clay dug out of the back field which is very common round there. Surprisingly they agreed to me digging a massive whole in there garden. Mum is a keen gardener and says she suffers from clay bound soil. So digging a massive hole would loosen up the soil and be really good for her plants. Result…

I think we measured took about 13 3 gallon buckets of clay when we finally hit pure stuff. which turned out just enough.

Making test bricks is a really good idea. All clay is different (unless you buy it pure I imagine). If you mix up enough clay and sand to make a 1″ thick brick shaped lump of clay out of pure clay, 1:1, 1:2, 1:3, 1:4 using more clay. The clay is made up of very fine particles and fills in the gaps between the sand. It stops it shrinking and cracking. Use a ruler and score two lines on the bricks 10″ ish apart. When they have dried out naturally (dont rush it) You can see how much the bricks have shrunk and cracked. The mix you choose should be hard and not crumble but not have not shrunk by more than 2% in length.

After making some test bricks I came up with a ratio of about 1-1 sand and clay. I think there was a lot of sand in the clay when it came out of the ground.

p.s. I just went down to the builders yard again for the sand. you need a lot. enough to mix with the clay to make a building mix and make the sand form for the dome. Because clay is made of very fine particales that when mixed with sand, fill in the gaps between the grains of sand. So 1 bucket of clay + 1 bucket of sand does not equal 2 buckets of building mix. Again you will have to trail and error the amounts.

Build Day

So after marking out the shape of the oven on the bricks wit marker pen (so you can still see it when wet) I piled up sand in to a form. using a stick 16″ in height stuck in the middle of the form. So when you start to bury the stick you know the exact height. Kiko Denzer in his book says it is really important to get the ratio of height to door height right apparently. 16″ seams the ideal height which at a ratio of 63% gives a door height of 10″. It is all in the Kiko book. Shape the sand into a perfect dome nicely compacted down. Then layer the finished sand form with damp newspaper. This is so when emptying it you can feel where to stop digging the sand out.

Now comes the clay sand mix. No straw like in a traditional cob mix which gives it strength. In an oven straw just leaves gaps and air which you don't want. You want supper compacted clay and sand for thermal mass. To make the mix you spread out a big tarp and cover it with a couple of buckets of sand and in my case a couple of bucket of clay (broken up in to little wallnut sized bits). Then tread it into to each other with your feet. If you have made pastry it is very much like rubbing the fat into the flour. You need to really thoroughly mix them together. A tarp come in really useful to do this as you can turn it all over really easily by pulling one side of the tarp to the other (the bigger the tarp the better). When you think it is all mixed in really well do it a bit more. add a bit of water till it holds together but doesn't splat when dropped from a waist height and you are ready to start building. You are going to do this a lot of times before the day is out. You want to build the first layer all in one go so you dont get and dry joints which will crack under high heat.

Grab a hand full of mix and compact it down into a solid ball in your hand. build it up this way hand full by hand full (4″ thick) until you reach the top. My mix was a bit wet and it started to sag slightly. So the higher we got the thicker the bottom got. So by the time I got to the top the bottom was about 7″ thick.

Dome

It looked a bit of a mess at first and I was a bit worried. Until when we had finished I got my plastering trowel out and with some elbow grease and it came up lovely. it looked like a massive one of those marshmallow chocolate teacake things.

Undoubtedly, you would use your wood fired clay oven for more than just emergencies.

In a survival situation or emergency, however, having this available is one way to ensure you can cook even if the power goes out and because it is an oven, you can diversify the types of food you can cook.

To learn more about this and other projects, please visit Instructables.