A step by step guide to building a Clay oven

As part of our Earth and Sun Energy Learn and Create course in August 2009 we built a  “clay oven”, “traditional clay oven”, “wood fired oven”, “pizza oven” and a “traditional bread oven" or whatever you want to call it(!) on our newly aquired land.  The great thing about building the oven on the land was that  most of the materials needed for the build were right there . Water, sand and pebbles from the river, rocks from the surrounding mountains and clay from the ground. In fact the only material used for the build not from the site was some old bricks. The whole process was entirely satisfying from collecting materials to tasting the first cooked morsels.   Here are photos and instructions for you to use should you want to have a go.

  To see the picture of the oven we built click here      

What will you need?It is possible to build your oven from a variety of materials ,the list below includes the materials we used.

Materials

River/Beach or Builders  sand Clay Large Stones for base   Water Rubble /pebbles / hardcore   Normal building bricks for oven base   Old Newspapers   Wood for burning in the oven

Equipment 

Wheelbarrow Buckets Tarpaulin or thick plastic sheeting Shovel Spirit level Large knife Hands and feet! Wellington boots or other sturdy boots

The beauty of building your own clay oven is that it can be done using scrap and salvaged material and in our case from local  natural materials. You needn't spend anything on it at all except a little of yours and your friends or family's time.

 

Step 1: Building the baseBuilding a good, strong, dense and well-insulated base is very important. For the oven to work, it needs to absorb as much heat as possible and get up to temperature... allowing it to lose heat will only slow down the process.  

Dig a foundation. 40cm deep ,125cm x125cm.The sizes are dependant on how big you want your oven to be. This size will give you a familly sized oven

 

 Fill foundation with rubble ,we used pebbles from river but any masonary rubble will be

ok. 

 

Place large  stones (with or without mortar) in a circle and  fill in the circle  with  river pebbles or other rubble  and than build another ring on top of that untill you have built a

stone circular wall filled with rubble about 2ft tall. Compress the infill by treading it down  and than pour sand over the top  and level.  

  

 Place the bricks level on top of the sand making sure you have 2 bricks overhanging where your oven door will be .This is to easily remove coals and makes a good shelf.

 

 Bind the brick oven floor to the stone base using clay.

 

  You will not be able to move the oven once it is built, so plan where you want to site your oven carefully. Think about proximity to food and water ,which way the prevailing wind blows from(better to have door facing away from this) and a shelter from the elements.

Step 2: Creating the sand formTo achieve the dome shape you need some sort of mould, template or shape to support the clay,  we chose to build a sand form. Simply create a dome out of sand, the size you will want the inside of your oven to be.  

When  the sand form is completed cover it in wet newspaper in preparation for the clay. We Forgot to get a photo at this stage but you can see the idea with the below photo

taken from another project   

   

Step 3: Preparing the Clay and building up the clay over the sand form

Finding the right mix  

 

After taking 6 soil samples from the surrounding land we were lucky enough to find a suitable clay soil ready to use. 

 

 4 of the  samples contained too much silt and not enough clay and 1 mix was almost pure clay. The silt cannot be worked with  however if you have a good source of clay all you need to do is add the correct quantity of  sand to make it usable. There are various simple tests that can be carried out to find the correct mix.  The Drop Test Mix up a little of your mixture or soil  with some water than grab a handful of mixture and work it into a small ball. Always add small quantities of water as a very wet mix will not give a true impression of your mix untill it drys out a little.    

1. Hold your arm directly out in front of your body at shoulder height.   2. Drop the clay-sand ball onto hard ground in front of you.

The ball should hold together quite coherently.  If it splats flat the mixture is too wet or you have too much clay and you should add more sand to dry it out a little.  If the ball breaks to pieces it is too dry or you have too little clay in the mix so you need to add more clay or water.  Simple! When you squeeze the ball next to your ear you should be able to hear the grains of sand rubbing together ,if you cannot add more sand untill you can and repeat the test.  

Once you are satifised you have the correct mix than you can proceed with preparing the mix for the oven which is basically breaking the lumps up and adding water .

 

     Now you are ready to start building the clay oven walls . This part of the process is quite critical and should not be rushed. What you are aiming to do is follow the shape of the

sand form, without actually putting any real pressure on it, as otherwise you risk deforming your sand form and ending up with a funny looking shape which was the case

with our attempt but we got there in the end . 

 The best thing is to take chunks of clay at a time, working from the base up, and working your way around the oven gradually. Make sure you bind each piece of clay to the one

you are adding it to, and put plenty of pressure on the clay (but not on the sand!). 

Make sure you keep the same thickness throughout, we did this by deciding on a number of fingers of thickness we wanted, and making sure it is the same thickness right the way

around. Once done, smooth off the outside of the oven.

 

Step 4: Carving out the door and scooping out the sandOnce you have given the oven some time to firm up and applied some decorations, you will want to carve out the door. The key magical number here is 63. The height of the door needs to be 63% of the height of the inside of the oven. If you make the door shorter the smoke won't evacuate and it will suffocate the fire. If you make the door too tall, the fire will burn too quickly and lose heat. This is a key part of the process,  so take time when planning the size of your oven.

Once you have worked this out, carve the door with a sharp knife , and let the oven set a little more for another 3 or so hours.

 

 You are now ready to remove the door and scoop out the sand. The newspaper was put in

there as it will stick to the clay and is a good indicator that you have reached the clay and do not need to dig any further to remove the sand. No need to remove the newspaper

unless it comes away easily, as it will burn off when you first fire up the oven. 

If you have the patience and whilst the inside of the oven is still soft, use your fingers to smooth the clay surface off, just as you did on the outside.

Step 5: Let it dry!!! And fix and cracksWe cannot stress enough how important it is that you give the oven time to dry. Be patient! If like us you choose to light the fire too early, you will risk causing more cracking and making the oven more fragile, so give it a week to dry off naturally.

It is inevitable that the oven will have some cracks. See below for a section on cracks. Do not worry about these, just patch them up with some of the fresh clay you had left over from building the oven. This will not affect how the oven will perform that much so you needn't lose any sleep over it.

Step 6: Light your fireThis is it!! You have put in all the work, taken the time to let it dry, and it should now be feeling very hard, dry and strong. It will have shrunk a fair bit as well, but no need to worry.

We use a variety of wood to fire the oven with .

Ensure the wood is:

- Dry and well-seasoned: if the wood is not dry, it will introduce moisture into the oven, which will slow the oven from heating up, and could damage the oven as well.

- Untreated: If using scrap wood, make sure it has not been treated, as some chemicals used in the treatment of wood are very harmful and you don't want them anywhere near your food.

- Small: Ensure you cut your wood so that it is kindling-sized. We have heard different bits of advice about what types of wood to burn, etc.. but in our experience the smaller the wood, the quicker it will burn and therefore the quicker it will release it's heat, which is what we want.

Step 7: BakingYou are all set! You will need to carve some sort of door for the oven, and the rule of thumb is that whilst you can cook pizzas in the oven by pushing all the embers to the edges and giving the base a quick brush, you would normally get the oven really hot, remove the fire, put your bread in and seal it with the door if baking bread or loaves.

 

A word on cracking

Don't panic!!

Cracking is a natural process. More or less cracking will occur, depending on how much water you introduced into the clay to get it soft enough to work with, and how quickly the oven dries out.

As it dries, the clay will contract, the oven will shrink away a little and cracking may occur.

 

To avoid cracking, ensure you do not rush the drying out and give it as much time as possible. Do not attempt to dry the oven by lighting a small fire in it unless you are pushed for time; and if the sun is shining consider covering the oven so it is left to dry in the shade.

Once the oven looks like it is dry, use some of the clay you kept aside and fill the cracks. You may have to repeat this process a few times as the clay you will fill the cracks with is likely to crack itself. Do not lose patience, it will sort itself out in the end.

 

TOP TIPSThese are just some tips we picked up along the way, so thought we would share them with you.

- Plan the size of your oven carefully, ensuring you measure the height of your sand form when it is done so you can work out what the height of the door will need to be.

- Ensure you have kept some spare clay aside to use to fill any cracks.

- Make sure you have all your wood for burning ready, cut to size and dry.

- Get yourself one of those oven thermometers so you can put them in the oven and monitor the temperature -You can add extra insulative layers of clay and straw once the first layer has totally dried. This will hold the internal temperature for longer   

For more information and projects from Permaship visit our website

https://sites.google.com/site/permaship1/Home