Well it has been a long time in the making and an even longer time in the dreaming about, but it is finally done.... Just in time for winter. Doh. Oh well better late than never.
I have been dreaming about building my own oven for ages now. I started talking about how much I would love to build one when I was renting a two bedroom flat. So I couldn’t really make one then. A couple of years after that we moved to a house, but were still renting and I wasn't going to spend all that effort improving someone else's garden. My girlfriend (Now wife) one Christmas got me all the pizza tools and booked me on the "Build and Bake" course at river cottage. She also got me a copy of "Kiko Denzer - Build Your Own Earth Oven" Which I read cover to cover on the train many times and can’t recommend highly enough. There was no turning back from that point. Finally last year we bought our own house and I could finally build my oven I had been dreaming of all this time!
Step 1: Base
First the base..... I poured a concrete slab and set to building the walls, both of which were a first for me. I was going poor a slab of concrete but saw these small lintels at the builders merchant and laid 4 square flag stones on top that had been left in the garden when we bought the house. I wanted to store wood under the oven as we don’t have a lot of space for a separate wood pile. Thinking about it later I wish I had left the back open so there would have been better air flow around the wood keeping it dryer. Instead in the finished oven you can see I have chopped down a wooden pallet to fit in the bottom, so the air can circulate.
Step 2: Fire Bricks
I picked up some fire bricks from http://www.kilnlinings.co.uk (found through the fantastic http://ukwoodfiredovenforum.proboards.com/index.cgi, thanks guys, lovely bloke really helpful) 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.
Step 3: 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.
Step 4: 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.
Step 5: 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.
Makeing 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 particals 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.
Step 6: Build Day
Build day! As my parents were so happy to help me dig up some clay I thought I would push my luck and rope them into treading some mud. It is a long day and I was glad of the help. I would never have done it on my own. Thanks Mum, Dad, Claire and baby rosemary for all your help.
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.
Step 7: 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.
Step 8: Drying
It was a really wet summer, I don’t know if you noticed. When I was trying to dry it out was one of the wettest parts. So it took forever to get to a point where I was confident it wouldn't collapse. It was about 3 weeks in the end because it was under a tarpaulin most of the time. When I did open it up and pull all the sand out I also cut back the wall a bit and put in a brick arch (only house bricks though forgot to buy fire bricks for this bit). Also I had a good look at the inner surface of the oven and smoothed out and deformities or cracks with a bit of water and the back of a spoon. The smoother and uniform the inner surface of the oven the better.
Then more drying and waiting... It is SO tempting to light a fire in there and just heat it up and be done with it. Slowly slowly catchy monkey. Just air drying then a few days later couple of tea lights. Then some of those big chunky candles going for hours on end. Then a small fire with kindling. Then next night I tried to do another small fire but it got a bit large and dried it out but some hairline cracks appeared. Next time small fire and decided it looked pretty dry, so cranked it up. I got some cracks about 5 MM on the outside appear but nothing on the inside. Pizzas were good but I don’t think I got it hot enough. and maybe some moister was still in the walls. It took about 5-6 mins to cook a pizza. I am sure I can get that down with more drying and with the insulation layers added.
The final two layers were one of clay slip with sawdust (Nice and loosely packed with loads of air pockets for insulation about 4" thick). When that layer had dried I applied a thin layer of clay, sand and straw mix for plaster (About 1" thick with a very thin coat without the straw to give it a smooth finish).
Step 9: Roof
Finally I built a little roof for it with a removable front so it wont go up in flames. I was really fed up of having a tarp in the garden right outside of my kitchen window. You really need to keep it covered or it will turn back into a pile of clay and sand in the rain. The dome is a lot dryer now with the ventilated roof, I think the tarp was keeping in the moister, much like cling film would. My wife is now calling it the pizza hut, not sure if I like being linked to that establishment but it is better than my mates at work who call it a dog kennel. I really enjoyed making the roof. It was the first time since A-Level Design Tech that I had done any project like this. The amount of cuts on my hands are testament to that.
So I finished this afternoon just in time for winter to hit... oh well couple of weeks the wife and I are hosting a pizza party. So I have got to get the hang of using it before then.
I am no in no way calling myself an expert. I just read a lot about it for a long time before I had a go at it. I hope this helps any of you if you are thinking of doing your own.
If you need any help get yourself over to http://ukwoodfiredovenforum.proboards.com/index.cgi There really is a forum for everything on the internet. There is a wealth of information out there.
p.s. I have full CAD designs for the base and roof if anyone wants them. (I did say I had a lot of time to plan this)
Step 10: Update: Door
I finally decided to bite the bullet and make a proper door for my oven. I have been using the form (see below) that i used to make my arch. but as well as it not looking very pretty there were a lot of gaps for air to pass through. you could feel it pouring out with your hand. after all this effort insulating my oven letting all the heat out makes no sense. I picked up a flue thermometer from Clus Olssen which is an amazing £8.49.
It is all wood and has no real protection. It is only meant as a bake door as I have not chimney so cant fire it with a door on so there will be no flame in the oven when it is being used. So I am not worried about it burning too much.
I glued and doweled together three pieces of 4" x 4" fence post I had left over from building the roof for my oven (best £20 I ever spent on ebay still got enough for a prep table). I cut it large then using a electric planer skimmed off the edges at a slight taper till I got a perfect fit. The handle is also carved out of off-cuts of the fence post.
I added some stove rope in a routed gully just to give it an extra seal.
I kind of like the massive probe. My only worry with this project is that because the first 4" are encased in solid wood so the whole of the probe is not exposed to the full heat. It works really well. I let it get down to normal oven temps and put a kitchen oven thermometer in it and it was bang on the money.
Step 11: Cooking
Step 12: Recipe
The Pizza Recipe is a whole instructable on its own but this is an outline of what I like to do....
Napoletana Pizza Recipe makes 4 10" Pizzas
10g Salt (1 3/4 Tsp) Table salt
3.15g (1 Tsp) instant yeast
450ml cool water
Mix the flour, salt & Yeast together well (making sure that the salt and yeast do not come into contact) add the water all at once and mix to a shaggy ball.
Leave it for 5 minutes for the flour to become fully hydrated and gluten to start to form.
Now knead for 10 minutes or until the dough will pass the windowpane test. (stretch out the dough thinly, it should form a thin skin that will support your finger without ripping)
divide the dough into 4 balls (about 275g each) and place into individual oiled tupperware containers.
leave out for half an hour then put in the fridge overnight.
an hour before baking take them out of the fridge and let come back to room temp. They will have already risen.
1 1/2 tins (400g) crushed Tomatoes / Plum tomatoes drained of most liquid
clove of garlic
1/2 Tsp of red wine vinegar
salt & Pepper
1/2 Tsp Oregano & Basil (fresh if you can get it)
Either lightly blend the sauce with a stick blender or just crush with your hands. there is no need to cook the sauce as the tomato is cooked in the can. the beautiful fresh tomato flavors will be lost if you overcook it.
Topping combinations I really like
Saute some mushrooms with garlic in a frying pan
Fresh Cherry Tomatoes with Artichoke hearts and feta cheese
Olives, Capers & Chilli Flakes