My clay oven is now almost one year old and, to be honest, it was starting to look it!

The last time I fired her up I noticed that the cracks in the outer layer had grown substantially and, disaster upon disasters, the following day I noticed what I thought was steam streaming out of a crack at the back.  In fact it turns out that the oven was on fire!!  It seems the cracks in the outer layer had penetrated deep into the insulation layer which, happy with its new source of oxygen, subsequently caught fire.  After dousing the smoldering mass with water I decided it was time to do something about it.

This week I repaired the broken chimney (see photo) and filled all the cracks with a new load of sand/clay mixture. There is nothing difficult about this.  Just make up the mixture as per the usual method.  Remove any damaged/friable bits of your oven.  Wet the area you are working on so that the new mixture can bind to the structure more easily. Mould and fill cracks as required.  Simplicity itself!

I have fired the oven since repairs and of course cracks re-appear (part of the normal expansion of the oven) but hopefully it should extend the lifetime of the oven a while longer.  We’ll see!

After several weeks of receiving many questions from Clayoven visitors regarding where to find clay and specifically what type of clay one should buy from potters suppliers, I decided to ask an expert.

Sue works at Briar Wheels (a supplier of all things pottery related based in Fordingbridge, Hampshire) and knows a lot about pottery clay (useful in her profession I guess!).  Last week I cheekily asked her if she would like to write a small post for the blog about different types of pottery clay and she kindly said yes.  This is what she had to say:

There are 2 main varieties of clay, Earthenware or Stoneware.  This divide is depending on firing temperatures. Earthenware clay is fired in a kiln at a lower optimum temperature (maximum of approximately 1160ºC) and Stoneware clay is fired at a much higher optimum temperature (maximum approximately 1280ºC)

For building a Clay/Pizza oven, although the clay is not going to be kiln fired, the heat from the actual firing is enough to heat the clay right the way through, so Earthenware clay is the usual clay to purchase.

Prepared clay bought from a Pottery supplier will be ready to use, all impurities such as stones etc. will have already been extracted.  The last thing a production potter wants to do is mess around with the clay in the first place making it fit for use! So it will have gone through a process of pugging and will be ready to use straight from the bag.
Pottery clay comes in many different colours and grades from a very fine clay for detailed sculpture work to what is known as a heavily grogged (particles of already fired clay) clay which is suitable for handbuilding and is what I would suggest for the Clay Ovens.  Grogged Terracotta Clay is mostly sold for the making of Clay Ovens as it has about 10% grog and when the clay has dried out, and has been fired through, is a lovely warm colour. Extra grog or sand may be added to the clay if required, although many people use it just as it is with good results [I would still reccommend that you use a sand/clay mixture for your oven at the normal ratio of 2:1 sand:clay, grogged or not! - Simon].

Clay is usually sold in 12.5KG packs and depending on the size of Oven required may take 10 – 15 bags to complete the project [I cannot verify this becuase firstly I didn't buy clay for my oven and secondly I never weighed out the actual amounts I used - Simon].

So now you know.  How fabulous is that – thanks so much Sue!

Of course, in the interests of fairness I would add that there are other pottery suppliers out there who will also supply you with potters clay.  However, I’m sure none of them will be as super friendly as Sue and the team at Briar Wheels.  In return for her aticle I promised Sue a gratuatous plug, so if haven’t done so already, here you go!

Briar Wheels super friendly potters suppliers

A break in the rain clouds offered me the rare opportunity to fire up the oven last weekend so I decided to take full advantage of the interlude to cook-up a roast to die for.

The clay oven is fabulous at high temperature for cooking the perfect pizza but if you allow these babies to cool down somewhat, you can use the residual heat to cook sublime roast joints of meat.  It is the way that the ovens cool that creates the ideal temperature profile for cooking perfect roasts.  Last weekend I decided to try roasting a whole leg of lamb and, of course, I recorded the whole thing so I could share it on the blog.

The spices make this leg of lamb yellow!

Stage One: Prepare your joint of meat
Normally, with a joint of free range, organic meat I would suggest doing very little with it.  With lamb, maybe some garlic, fresh rosemary, a splosh of olive oil and some salt and pepper.  This time though my wife marinated the lamb over night in a mix of Moroccan spices (a Nigella Lawson recipe I think).  I recommend trying this if you fancy something a little different – it is truly delicious.  Whatever you decide to do make sure your lamb is prepared and ready to go.  Place the joint of lamb in a roasting tin and keep covered at room temperature until you are ready to cook it.

The oven reaches 350 degrees C

Stage Two: Fire her up!
Firing the oven for a roast is no different to firing it up for cooking pizzas.  Follow the technique I outlined in this earlier post.  Keep the “full blaze” fire going for a good hour or so because you want residual heat in the whole oven structure – in the bricks and the walls of the oven itself.  You can see from the photo that on this occasion my oven reached 350 °C (it took around 2 hours 15 minutes to reach this temperature).  You may think that this is relatively cool and you would be right!  This was the first time the oven had been fired since last year and so it had a whole winter’s worth of moisture absorbed within it which had the effect of lowering the maximum temperature.  Not to worry though! If you were to put a joint of meat in the oven at this temperature it would be cremated in minutes!

Stage Three: Wait for it!
Allow the fire to burn down.  You can help this along by spreading the embers across the oven floor.  At this stage you need to keep your eye on your temperature gauge which will slowly begin to drop.  When the temperature reaches 260 °C put the tray, together with the joint of meat, into the oven.  Leave the door and chimney open for now.  Cooking the meat at this high temperature for the first part of the roast is what Hugh Fearnly-Whittingstall calls the half-hour sizzle and is a crucial part of the roasting process.  Over the next 15-20 minutes or so the temperature will slowly drop.  When the oven temperature drops to approximately 190 °C, block the door and the chimney.  Leave it like this until the meat is cooked.

Cooked to perfection

How long does it take?
Well this obviously depends on the size of the joint of meat and the type of meat you are cooking.  I cooked this leg of lamb for 1hr and 40 minutes after the door and chimney was blocked.  When I took the joint out, the oven temperature was still at 170 °C.  It would have stayed hot for many hours longer so, if your meat needs a little more cooking time, whack it back in!

That’s it.  Simple eh?  Any meat cooked in the oven in this way is mouthwateringly moist, extremely tasty and just falls off the bone.  You should also try chickens (complete with roast spuds) and my favourite, belly pork which is truly sublime! Try it for yourself and let me know how you get on.

Happy roasting!

Pizza cooking in the oven

I’m not exaggerating when I say that pizza cooked in a fiercely hot clay oven is the best you will ever taste. Why are they better than pizzas cooked in the gas or electric oven in your home?  It’s all about the heat!  The oven in your home will reach a maximum temperature of around 250° C.  A clay oven, fired for a few hours, will reach temperatures well in excess of 400° C and it’s this furnace-like heat that turns a thin circle of dough, topped with oil, meats and cheese, into an absolute gourmet treat! Pizzas cooked in a clay oven take no longer than 2 minutes to cook.  They have thin, crisp and slightly charred bases while the toppings remain delicious and full of flavour. Is your mouth watering yet?  Mine is! so lets get on with the main thrust of this post which, if you haven’t guessed already, is about making pizzas in a clay oven.

Firstly, if you want the best pizza ever you really need to buy the best ingredients you can get your hands on. Make sure you buy good quality flour, organic if possible.  Dried yeast is perfectly adequate so don’t worry about trying to get hold of the fresh stuff. The toppings are crucial too so don’t scrimp and buy cheap ingredients – you don’t need masses, so splash out and treat yourself to quality.  The following recipe is borrowed/copied from Dan Stevens, a chef from River Cottage HQ (Dan has recently written the River Cottage Bread Handbook which is due for release anytime soon I hope!). 

Dough (this is enough to make at least 15 small pizzas)

250g strong white bread flour

250g plain flour

350ml warm water (room temperature)

5g dried yeast (10g of fresh)

10g fine salt

A glug of olive oil

Add all of the dry ingredients to a large mixing bowl and give it a quick mix.  Next add the water and mix into a rough dough. Finally add the oil and squidge it well into the dough.  Flour a surface and tip your dough out onto it – it’s time for kneading! You can use a electric mixer with a dough hook to do this if you prefer but I like to get working on the dough with my hands – it just seems right somehow! You will find that this dough is quite wet (sticky) compared to traditional bread dough.

A tip about kneading. There are lots of methods you can use for kneading dough but I like to use this one (again thanks Dan at River Cottage). Hold the dough ball to the surface of your table with the tips of your left hand. Then with the heel of your right hand placed in front of the fingers of your left, push the dough forward, stretching it along the surface top then, in a fluid motion, pull the dough back towards your stationary left hand. Rotate the ball and repeat. I normally knead for about 10 minutes or so. Lightly oil a large bowl, put the dough into it, cover with clingfilm and leave to rise until it is double the original size. That’s it – dough done! 

Toppings

Ingredients at the ready

The choice of toppings is totally up to you but here are a few essentials as far as I am concerned:

• A mixture of olive oil, crushed garlic and herbs is, for my money, a much better pizza base topping than the traditional tomato sauce.  Just drizzle or paint it over the surface of the dough before you add the rest of your toppings – it’s delicious!
• Grated cheese (mozzarella, Gruyere, Cheddar)
• Chunks of other cheeses (buffalo mozzarella, blue cheese)
• Mixed cured meats (spicy sausages like salami and chorizzo chopped or sliced, chunks of good organic ham)
• Roasted artichoke hearts
• Fresh basil
• I would have suggested anchovies to give that powerful salty, fishy blast but unfortunately anchovies stocks are in crisis due to over fishing so I no longer buy them – I suggest you do the same for the time being.

Other things you’ll need (ideally)

• A rolling pin
• A wooden chopping board
• A bakers peel (pretty much essential)
• A sharp knife

Making the pizzas

One of the best things about making pizzas outside using your own clay oven is building your own pizza – rolling out the dough, selecting various topping mixes from pots of delicious, fresh ingredients, sliding it onto a peel and finally into the hot oven.  It is enormously rewarding and great fun so I always get everything ready outside then let friends and family make-up their own pizzas as they go – trust me everyone loves it! The process is simple:

1. Make sure your oven is really hot.  I normally fire mine for about 2 hours before cooking. Leave a fire burning at the rear of the oven and keep feeding this throughout the cooking period with extra wood.  Scrape clear the floor of your oven.  I normally push any embers to the back of my oven using the upside down blade of my bakers peel. 
    
2. Grab a small piece of dough and roll into a rough ball – about golf ball sized should do.  I prefer to make smallish (maybe 7-8″ diameter) pizzas because they are much easier to handle in and out of the oven.
    
3. Flour your rolling surface and rolling pin well but don’t over do it with flour.  You need enough to stop it from sticking to the surface but too much and it burns on the base of the pizza once in the oven.
    
4. Roll the dough out into a very thin disc (mine often come out in strange “country” shapes but it doesn’t matter).  Add more flour if it sticks.  Critically you want to ensure the base is NOT sticking to the surface because you will have all sorts of problems getting it onto your peel once the toppings are on otherwise.
    
5. Paint or drizzle the base with the olive oil or traditional tomato topping.
    
6. Throw on your toppings.  Hint: don’t pile too much on your pizzas because toppings have a tendency to fly off when you slide the pizza from the peel into the oven!
    
7. Slide the pizza onto your bakers peel – I find if you lightly dust it with flour first, then lift one edge of the pizza and with a quick, fluid movement pull it onto the peel.  Practice makes perfect!
    
8. Next you need to slide the pizza from the peel onto the hot floor of your oven.  Again you might not get this right the first few times but persist and you’ll have it cracked!.  The technique you need to master is “yanking” the peel from underneath the pizza  - very much like pulling a tablecloth from underneath a fully laid table without breaking the plates or spilling the drinks!
    
9. Let the pizza cook for about a minute – keeping a close eye on it.  I normally then slide the peel underneath it, take it out of the oven and rotate it through 180° so that the side that was facing the open oven entrance is now facing the fire burning at the back of the oven and vice-versa.  You might end up with a pizza burnt on one side if you fail to do this.  Pop it back in for a little while longer until you are happy that it looks cooked.
    
10. Slide the pizza out of the oven onto the peel then transfer onto a wooden chopping board.  Slice and serve.
     
11. Savour the best pizza ever and feel smug that you have created such a spectacular thing!
     
12. Repeat until you and your guests can’t move for eating pizza.

I’d love to hear how you get on and maybe you can also share some of your own pizza recipe ideas.  

Good luck and happy eating.

The finished pizza. This photo does them no justice whatsoever!

Burning Kindling in the oven entrance

I discussed the process of firing the oven in a previous post but I thought it warranted its own posting because if you don’t get this right – you wont be cooking anything!

This is the way I do it.

1. Prepare a nice big pile of kindling
    
2. Roll some balls of newspaper and pile them just inside the mouth of the oven in a cone shape
    
3. Pile kindling sticks around the newspaper like you are constructing a wigwam
    
4. Light the newspaper and let the fire catch.  Now at this stage I have a handy cheat that you might find useful.  I have a weed burner which I bought a few years ago and never used and it is perfect for getting these fires going in the oven.  It isn’t very Eco-friendly through so I won’t encourage you to buy one but if you have one lying around and some spare gas then go for it!
    
5. Gradually keep adding kindling to the small fire until it builds to a nice little blaze.  At this stage you can move it a little further back into the oven.  I push the fire using a shovel or, and I find this works well, my bakers peel.
    
6. The process is then to gradually add more wood (gradually larger pieces) and when roaring, push it back more until the fire is blazing near the back of the oven.  This might take about 40 mins to an hour.  Be careful when you are pushing the fire backwards as it has a tendency to go out.  If you find it has died back try adding some small pieces of kindling and blowing and/or some balls of newspaper.
    
7. In order to get the oven up to temperature (and I mean so that it is capable of retaining heat, without a fire burning in it for several hours) you need to keep the fire blazing for at least another 1.5 to 2 hours.  If you intend to cook with a small fire still burning (how I cook pizzas), the oven will be ready after about an hour.
    
8. If you intend to remove the embers and use the oven without a fire burning it’s a good idea to spread the glowing embers across the floor of your oven for 10 minutes before removal.  I then scrape them out with the peel or shovel and dump them into a metal bucket to cool.

The fire is roaring at the back of the oven

Hot embers spread across the floor of the oven.

Finally a word of warning.  If you have any sort of hair on the front of your head and want to keep it that way WEAR A HAT OR CAP when you fire your oven.  You will need to keep looking into the oven and when it is throwing out 450-500 degrees Centigrade of heat you will singe your hair.  You may not find this as hilarious as my wife did! 

  The final layer. The oven is complete! 

So at last we reach the final layer.  Once the insulation layer is dry you can crack-on and finish your oven.

The last layer uses the exact same technique as the first layer so you should be an expert by now. Using the same proportions, mix a batch of sand and clay together applying the good old puddling technique described earlier.  Again, the amount you need depends on the size of your oven but remember that this last layer will require more than the first layer due to the greater surface area you need to cover.  You will also need some spare mix to extend the chimney (if like me you didn’t make it tall enough first time round!) and to keep for filling cracks.  Make “bricks” as before and gradually build-up the final layer. After you have inserted the last brick, pull-up a chair, open a cold beer and sit back and admire your work.  Well done, your oven is complete!  

Next time I am going to provide some pointers on firing the oven so you can get the best use out of it when cooking. 

Entrance dry? Chimney dry? Great! Let’s start building the next layer – the insulation layer.

What you’ll need:

• Some clay
• Some wood shavings
• Some water
• A bucket
• A wheelbarrow
• A spade
• A power drill and plaster mixer (optional)

The insulation layer complete.

First thing you are going to do is make a clay slip which is simply clay mixed with water. The simplest way to do this is to put some water in a bucket and slowly add chunks of clay, squashing, squeezing and mixing with your hands as you go. Alternatively you could add water to half a bucket of clay and leave it to soak for a couple of days. You could then squish-up the clay quite easily.  You are aiming for a consistency similar to that of thin natural yogurt.  

I spent quote a long time making my slip until I discovered a short-cut method using a drill and plaster mixer. It works really well but is very messy! Chuck your clay and water in a large bucket (or large bin) and blitz it with the mixer.  Job done!

Next throw some wood shavings into a wheelbarrow. I bought a huge bag of wood shavings from a local pet shop and I still have three-quarters left (any takers?). Add some of the clay slip and mix well with a spade or get your hands dirty. The mixture should be wet enough to form “bricks” similar to those you made for the clay-sand layer.

Build up the insulation layer using exactly the same technique as before. Simple! Leave it to dry and then you can move on to the last step in the build – woo hoo!

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.

Finally it is time to start building your oven. For this stage you’ll need:

• Builders sand
• Old newspapers
• Water
• Tape measure or long steel ruler
• Clay-sand mixture

You are going to build a large sand dome – the former which supports the first clay-sand layer of your oven. I really enjoyed this part of the process mainly because it provided a practical justification for the hours I spent building sandcastles on the beach with my stepson Thom when he was a little lad (to be fair it was usually me who wanted to build the sandcastles!).

Sand dome partly covered with wet newspaper.

Tip lots of sand onto the brick floor of your oven.  I’m not sure how many bags I used but I remember being amazed at how much was needed to build up the dome to the required dimensions.  Remeber the outside of this dome will form the inside dimensions of your finished oven.  The base (widest part) of my oven is the same dimensions as the length and width of the brick floor (80×80cm).  I decided to make the height of my oven approximately half that of the diameter (40-45cm). Build up the dome, moulding and sculpting with your hands until it is the desired height and a nice shape.  A top tip from Steve at River Cottage HQ is to keep checking the shape of the dome from above, so periodically stand on your plinth to get that birds-eye view! Once you are happy with the shape, firm-down the sand with your hands.

Sand former covered with newspaper

Next you need to add a layer of wet newspaper.  This makes removal of the sand from inside the cavity much easier later on.  It is a little tricky to get the paper to stick but persevere and you’ll crack it.  Thats the dome complete. Now you are ready for your first oven layer.

The First (Oven) Layer

If you are doing this alone make sure you leave 3 or 4 hours to build your first oven layer.  I made the mistake of starting in the early evening and ended up finishing it at midnight wearing a head-torch!

Take some of the clay-sand mixture from your wheelbarrow in cupped hands and form it into an elongated/rounded brick shape.  Press this first “brick” against the  base of the dome and compress it into place, with one hand holding it against the sand former while the other makes a “karate-chop” type movement (using a straight hand) against the “domeward” side of the brick. This creates a wedge-shaped “brick” (sloping towards the dome) which helps when adding layers above and also removes any air bubbles from the mixture which may subsequently expand and crack the oven. You are aiming for an oven layer that is approximately 7cm thick and the simplest way to keep check of this is to measure the bricks periodically against a marked stick or even a piece of straw.  Add another “brick” next to the previous one and, using the same technique, mold it into the first.  Repeat the process until you have laid “bricks” around the whole circumference of the dome.

First few "brick" layers.

Begin laying “bricks” on top of this first layer and continue, round and round, up and up, until you have completely covered the sand dome former.  Remember to keep checking the oven layer thickness as you go. Don’t worry if you end up with some variation in thickness – as you build the oven layer up you might find that the base widens out a little from the weight of “bricks” above.  Smooth and shape the oven layer into a neat, coherent shape and don’t forget to check from above.

That’s it!  Your first layer is complete.  You need to leave it to dry for a few hours before you cut the hole for the oven entrance – which I’ll discuss next.

The oven layer is complete!

So now the fun begins!  Before I get on to detailed instructions of how to build the oven I want to provide some details on preparing the all important building material – the sand-clay mixture.

Ingredients

• Builders sand
• Clay
• Water (optional)

Equipment

• Shovel
• Bucket
• Tarpaulin
• Thick plastic bags
• Wheelbarrow
• Wellington or other sturdy boots
• Legs!

You can buy builders sand from any building suppliers, some garden centres and DIY stores (e.g. B&Q). Either buy it in individual plastic bags or get a job-lot delivered – you will use quite a lot.  

What type of clay should I use?

I have had quite a few questions about the type of clay to use.  As far as I know you can use any type of clay you can get your hands on.  I dug my clay from a local farmer’s field here in Hampshire (clay overlying Upper Cretaceous chalk if you are geologically minded – maybe Paleogene?).  The team at River Cottage get theirs from a pond on site, in Dorset (I think it is Blue Lias).  If you can’t find any clay locally you could always buy potters clay which would be wonderfully homogeneous – free from large particulate matter.  Which reminds me, try to get clay does not contain too many stones – they are liable to form the focus of cracks in your oven if left in the mixture.  

Quantities

The ratio of clay to sand is 1:2 (one part clay to two parts sand).  I used a bucket as a convenient measure and found that one bag of builders sand almost filled two buckets which was nice!  

I think it is wise to make-up just enough mixture (with a little bit extra) to complete one layer of your oven at a time.  Why?  Well if you make up a huge batch (enough to complete your oven) it could dry out before you get a chance to use it if you get delays between layers (if it rains for example).  So how much do you need for one layer?  This will vary depending on the size of your oven.  For mine, if we define one “batch” as two buckets of sand mixed with one bucket of clay, the first (oven) layer took three batches (6 sand to 3 clay).  This left enough over to fill small cracks after drying and to begin building the chimney.  The outer layer required more mixture because it is covered a larger surface area.  I used four and a half batches for this layer.

Mixing or Puddling

Clay chunks distributed onto sand ready for puddling.

Mixing the clay and sand is by far the most tedious part of the whole build process.  What you are trying to achieve is a well-mixed material with no pockets of unmixed sand or clay and the only way to do this seems to be by using your feet.  The process is known as puddling and it goes like this:

1. Spread a tarpaulin out on a firm surface (double it over in case you get holes in it).  
2. Tip two buckets of sand in a pile onto the tarpaulin and spread out a little.  
3. Next, fill another bucket with clay.
4. Take a chunk of clay and break it into small pieces (thumb sized) and distribute them over the surface of the sand (like throwing broken-up pieces of mozzarella onto a pizza base!).  Take this opportunity to dispose of any stones or sticks you might find in the clay.
5. 

   Puddling Sand-Clay mixture with help from my dog Scout!

   Wearing your boots, start to mix the sand using your feet (puddling).  The best technique is to tread and twist.  I recommend putting some music on and get into the groove! Seriously, you will look pretty daft doing this but you need to twist – Chubby Checker sty-lee!  This is where a group of friends come in very handy.  Many feet make light work of puddling sand and clay.  It is great exercise though so keep reminding yourself how much good it is doing you when you start to get knackered and bored!

6. Keep mixing until the clay lumps have disappeared then add more clay chunks and get back to puddling.
7. Keep repeating this until the bucket of the clay is mixed into the sand.

I found it takes somewhere between 45 minutes to 1 hour to mix one batch.  One tip I discovered which speeds things up is make sure the sand is damp before you start mixing.  It definitely helps the clay mix in better (essentially you are coating sand grains with clay and water helps break down the clay bonds I assume?).  Add some water before hand if you need to but dont go mad with it!

The last thing you need to do is check that the mixture is of the correct consistency i.e. not to wet and not too dry.  You might be surprised at how sandy the mixture seems but this is how it is meant to be.  The team at River Cottage HQ had a great method for testing the consistency though which I will share with you.  

1. 

   Sand - clay ball after drop test. It held together just right!

   Grab a handful of mixture and form a ball about the size of a lime.  

2. Hold your arm directly out in front of your body at shoulder height.  
3. 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 and you should add more sand to dry it out a little.  If the ball breaks to pieces (explodes) it is too dry and you can add a little water.  Simple!

Once you are happy that your mixture is just right shovel it into a thick plastic bag to keep it moist while you mix the next batch.

If you are ready to start building your first layer I recommend shoveling the final batch into a wheelbarrow for ease of use.  Wheel it over to your plinth – it’s time to start building your oven!