5. The Oven Entrance and Chimney

Just a dome-shaped sculpture without the entrance and chimney.

You have completed your first layer and now you need to build a nice entrance at the front of it in order to get food in an out (unless you leave it as a dome shaped sculpture!). At this stage we will also be removing the sand former and building a chimney.

You should have left the oven layer to dry for at least 4 hours before you attempt to cut the oven door but don’t leave it so long that the clay-sand mixture dries too hard or you will find it tricky to cut.

The dimensions of the entrance are dependant on the dimensions of your oven. Generally though, you don’t want it so big that it effects the heat retaining potential of your oven nor too small so you can’t get anything bigger than a tiny pizza through it.  In the end I chose the width of my door based upon the width of a standard roasting tray and, as it happens, the width of the bakers peel I had bought.  Don’t worry too much about the height at the moment because you will probably adjust that later on once you have fired it.

The oven entrance removed revealing the internal sand former

Roughly mark the width and curve of your oven entrance and then, using nothing other than a carving knife, slowly cut it out.  It will probably come away in large chunks – a very satisfying experience!

This is the moment of truth! Get yourself a bucket and start to excavate the sand from within the oven layer. Don’t forget to keep the sand for later clay-sand layers. Hopefully you will be able to excavate the sand until you reach the newspaper layer on the inside of your oven without the dome collapsing.  Take it nice n slow but I’m sure you’ll be absolutely fine.  Remove as much newspaper as you can but don’t worry too much because it’ll burn off anyway the first time you fire the oven.

Firing the oven

Kindling burning in the entrance to the oven.

Next you need to dry your oven layer.  If you are lucky enough it will dry nicely over a few days in direct sun. However you should also fire the oven at least once to help the drying process but also to check the entrance is high enough to allow smoke to escape (see below).

The method for firing the oven is quite simple but do bear in mind that at this stage the oven will be rather damp and does not have a chimney so you might find it takes a little bit of perseverance to get the fire going. This is how I do it:

1. Prepare some nice “pencils” of kindling.
2. Scrunch up five or six pages of newspaper into balls and form into a rough pyramid inside but near the entrance to your oven.
3. Build up kindling around the newspaper as if building a wigwam.
4. Light the paper and hopefully the kindling will soon ignite.
5. Watch the fire closely and keep slowly adding more and more kindling until it starts to burn well.
6. At this point, using a spade, metal rake or even a bakers peel, slowly push the fire back a little into the oven.  Don’t push it too far because it is likely to go out.
7. Add more wood and when it is burning fiercely move it back some more.  Eventually you want the fire to be burning in the centre-back part of the oven.

Fire blazing. Note dry patches appearing on the outside of the oven.

A couple of tips here.  Firstly, take it slowly. If you try to move things along too quickly you are likely to extinguish the fire.  If it looks like it is going out, screw-up a few balls of newspaper and throw them in. This is usually enough to re-kindle the blaze.  Secondly don’t use large chunks of wood  – smaller pieces burn better.

At this point you can modify the height of the oven entrance if you need to.  Look carefully at how the smoke is moving.  If it is “pooling” inside the top of the oven you need to cut your entrance higher to allow the smoke to escape.

As the oven dries it will steam and might produce a few cracks.  Don’t panic!  Fill in any cracks with spare sand-clay mixture before you move on.

Building the Brick Arch

Now the oven layer is dry you can build the extension to the entrance.  Extending the oven entrance with bricks not only looks nice but it also protects the entrance from knocks.  

Simply build a sand former in the newly cut arch of your oven, extending forwards about one brick length. Place a brick either side of the former on the top of the plinth using some of the sand-clay mix as mortar to hold them in place.  Gradually build up the archway around the former using more of the “mortar” mix between bricks.  You might have to use quite a lot of “mortar” in order to produce the correct curve for the arch (as you can see in my photographs below).  The last brick should form the keystone of the arch.  Leave the “mortar” to dry a little then remove the sand former. Hey presto – a perfect arch!

The Chimney

You need to cut a circular hole in the top of your oven just behind the brick arch entrance.  I sketched a rough circle on the top with a pencil then drilled holes around the circumference in order to help with removal of the now solid “cement”.  Just tidy the edges up a little with a knife then build-up a small 20cm chimney around the hole using more sand-clay mixture.  Finally, close any gaps between the brick arch, the oven entrance and the chimney using the remaining sand-clay mixture. 

Entrance and Chimney done!  Leave it to dry before we move onto the next stage – the insulation layer.

Brick arch and chimney complete.

The brick arch and chimney from the front.

1. Building a Clay Oven – The Basics

[PLEASE NOTE THAT THE LINKS TO THE OTHER 7 PARTS OF THIS ‘HOW TO’ CAN BE FOUND ON THE LEFT HAND COLUMN. ALTERNATIVELY JUST CLICK THE LINK AT THE BOTTOM OF EACH SECTION TO GO TO THE NEXT PART]

Welcome to the first installment of building a clay oven.  This post will cover:

1. Background – including what is a clay oven?, what can you use it for? can I build a clay oven?
2. What you will need – Materials and equipment
3. The build order
4. How long it will take to build
5. How long will it last?

Background

The Finished Clay Oven in My Garden

I assume that most people who have found this site will already know what a clay oven is, however it is probably useful if I define what I mean by a clay oven for the purpose of this blog.  Before I do that though a quick word about nomenclature.  I will use various names for the clay oven interchangeably, these include “clay oven”, “traditional clay oven”, “wood fired oven”, “pizza oven” and “traditional bread oven”.  If you browse around the web you will also see the name “cob oven” being used – cob being a mixture of clay and straw (+ or – sand).  As I am not using straw in my build I will not use the term cob but will include it in my definition as this type of construction is probably the most ancient of all clay ovens.  Another name commonly used is earth oven.

In my definition then, a clay oven is any hollow, dome-shaped structure constructed out of clay, clay and sand or clay and straw, used for the purpose of baking and roasting food.  It has a brick floor and usually a chimney.  Most traditional clay ovens are built outdoors and may or may not be covered with a simple roof structure.  You will find some amazing examples of clay ovens, particularly huge pizza and bread ovens, built inside restaurants.  The oven I have built is much smaller but still suitable for cooking for large groups of people.

Clay ovens are amazing things.  They look incredible and create a feature in any garden, large or small.  The most important reason for having a clay oven for me though is for cooking.  If you have never eaten a pizza cooked at 450°C for 1 minute in a clay oven – you have never eaten a pizza!  Just imagine a thin, crispy, slightly charred base covered in hot melted cheese, olive oil, garlic, sun-dried tomatoes, dried cured sausage, smoked ham, anchovies…do I need to continue?  How about loaves of hot bread cooked to perfection, cracked open and smothered in real dairy butter or a large joint of lamb or pork belly cooked slowly with herbs over night in the oven’s residual heat, falling off the bone when you come to carve it the next day.  OK OK enough of the M&S style adverts already!  I think you get the picture.  Cooking in a traditional clay oven is wonderful, it feels different and definitely tastes different.

Building your own clay oven is not difficult.  I am by no means an expert when it comes to DIY but am normally happy to give things a go.  I have never built anything like this before but managed to complete my oven without any major disasters.  The beauty of building a clay oven is that you use mostly natural and, if you are lucky, recycled or free materials.  There is something very primeval about building one of these ovens.  The process is a direct link back to our ancestors who would have used similar techniques for cooking many millennia ago.  I thoroughly enjoyed building it! It is a very physical and tactile experience – you will handle and form every single piece of clay, sand and wood that goes into it and the finished product is something that you will be extremely proud of.

What you will need – Materials and equipment

OK lets crack on with getting this baby built!  Here I will list most of the equipment and materials you are going to need to build your own clay oven.  I will provide details such as quantities later on as I step through the build process.

Materials

• Builders sand
• Clay
• Water
• Rubble / hardcore
• Wood shavings
• Normal building bricks (e.g. London Bricks) for oven base
• Large wooden “beams” or bricks or stone for plinth (I used beams as you will see later)
• Cement if you are building plinth out of brick
• Right-angled brackets and screws if constructing plinth from wood
• Glass bottles (optional)
• Old Newspapers
• Plastic rubble sacks
• Wood for burning in the oven

Equipment

• Saw (chainsaw?)
• Wheelbarrow
• Bucket
• Tarpaulin or thick plastic sheeting
• Shovel
• Spirit level
• Large knife
• Hands and feet!
• Wellington boots or other sturdy boots

The Build Order

So you have your equipment and materials list.  Next I thought it would be useful to outline the order of construction.  This will also form the basis for the rest of the posts in this series, each post providing details for each stage in the build process.  Simple – I hope!  As you might have guessed already, I love a good list so here goes another:

1. The plinth foundation, plinth and brick oven floor
2. The clay-sand mixture and puddling technique
3. The dome sand-former and first layer or the oven layer
4. The oven entrance and chimney
5. The wood shavings and clay slip layer or the insulation layer
6. The final clay-sand layer
7. Firing the clay oven
8. Cooking in the clay oven

How Long Does it Take to Build a Clay Oven?

Construction involves quite a few steps and each step takes variable amounts of time to complete.  Probably one of the most time consuming processes is puddling (mixing with your feet!) the clay-sand mixture.  One batch (two buckets of sand to one bucket of clay) will take about an hour to an hour and a half depending on the consistency of the component parts.  If you get a group of people to help then obviously you can speed the process up.  Many feet make light work of puddling!  Building the oven layers is also very time consuming and you need to leave drying time between each layer if possible.  The other major factor which effect the length of time it takes to build your oven is the weather.  You can’t construct anything other than the plinth if it is raining and it does tend to rain quite regularly in the UK!

What with interuptions (both weather and non-weather related) from start to finish my oven took 6 weeks to build on my own.  However if you have a spell of good weather and a few helping hands (and feet) I think you could build one in a week.

How Long will a Clay Oven Last?

To be totally honest I have no idea how long it will last.  I have only had mine in my garden for a few weeks now.  The good people at River Cottage HQ suggest a couple of years but obviously this will vary by your location, local temperatures, weather conditions, air moisture content, the type of cover or shelter your oven is housed in, the amount of use your oven gets, the type of clay you use for construction and many other factors.  They are pretty robust but they are organic structures and they do crack after repeated heating and cooling.  This is not a problem if cracking only effects the outer layer – you can fill the cracks with spare clay-sand mixture.  However, once you get cracks in the internal oven layer then the oven’s days are numbered.  I say, don’t worry too much, enjoy it and use it and if it falls apart you can build another one!