Clay Pizza Oven

I've been meaning to make a clay oven for probably 10 years - then in 2020 the COVID-19 epidemic hit, which meant I had no excuses and so decided to bite the bullet.

Firstly I would say - put plenty of research into it! There are lots of blogs and instructions on the internet, some of them are great and some of them are... not so good. I also found when reading blogs to always question why they did things in certain ways. You're building something that contains fire... and lots of it so I err on the side of caution. Some blogs will instruct you to use wooden structures, there maybe nothing wrong with this if it's safe but in my mind making something out of wood with an unknown high heat is not the right thing to do, so always be safe.

Secondly I would say you need to invest time. Some blogs talk about making a clay oven over a weekend. I would suggest if you're laying concrete, bricks and clay then this takes time. Just the chemical process for setting concrete takes longer than a weekend so don't rush it - your pizza oven will look better for it.

Lastly; although you can do these things on the cheap, most blogs I've read have gone on to talk about replacing bits over a couple of years, so although I did quite a bit of scavenging I didn't skimp on some of the materials as I really wanted a pizza oven that wouldn't need replacing or fixing every other year. To me it makes sense to make something that will last longer.

• Bricks (and lots of them) I used around 140 reclaimed bricks
• Aggregate:
  • 15 x sharp sand
  • 10 x gravel sand (ballast)
• 5 x cement
• 6 x Metal rods
• Heat proof bricks - I used reclaimed bricks from a storage heater
• 10 x bags of red clay
• 1 x big bucket of natural clay (from the garden)
• 1 x big bag of wood shavings
• 1 x bag of sawdust
• similar sized bottles
• 1 x archway - I really recommend Vitcas
• 20kg Vitcas fire proof screed
• Vitcas fire cement
• Vitcas fireproof tile grout
• Vitcas Fireproof sealant
• Lime render

Optional elements would be decorative such as tile.

I was lucky enough to have a strong solid base to set my pizza oven onto already. If you need to set a base though, make sure you have a good 300mm of hardcore foundation and at least 200mm of solid concrete flooring.

If you're doing this first be sure to use a 1:6 concrete/ballast mix and level it up. Set it in fine weather and if it rains make sure you cover it. Water the concrete with tap water every day (this actually makes it more solid in the curing process) for about a week. It's also worth pointing out that tap water should always be used for hardening mixing and hardening cement or concrete.

This first thing I did was just lay out the brick on order to get a good idea of the space I would need but also get some good measurements in place for what I needed to work with. This then helped to draw up some templates. Again I've seen a few blogs where people have winged this part but it's always led to complications further down the line.

You can download my PDF for free here

I love brick laying, I wouldn't say I'm a great at it (in any way) but there's something about watching a construction going up gradually - a little bit like making a really heavy cake.

I had foraged a good 180 bricks from various different places over the years specifically for this project. The result is a shambolic mismatch but this is the look I'm going for - I want the oven to look rustic. The only issue I would say with doing this; is bricks vary in size, so if you go down this route make sure the outside edges are sharp, level each layer and be aware you may have uneven gaps in between bricks.

I used a one brick thickness structure all apart from the entrance because I wanted to have a solid front specifically to hang some doors for my dry wood storage. But I also wanted to suspend a concrete floor which would take the stress of the large entrance to the oven. I built mine up to 9 layers, set my concrete slab and then set another row of bricks for my clay and bottle insulation (Step 4).

For those that haven't done bricklaying before I would suggest looking at youtube videos to get some idea of the process - a good recommendation is Rodian Builds who talks through the basics.

This took some prep but it was well worth doing with precision.

Firstly I built a wooden frame on the inside of my brick structure - roughly 1 brick down from the top (step 1) and then laid some floorboards on top of this (step 2 image).

Then I made a frame which held to the outside of the construction - again roughly 1 brick high (step 3). Tip: I sealed the edges/gaps of the bricks and outside wooden frame with spare clay - this could then be taken off when the framework's removed.

I then poured half of my concrete mix into the framework and laid steel rods into the structure using the outside walls as supporting structures (3 horizontal and 3 vertical). The rest of the concrete was then added and I spent the next hour levelling the surface and making sure as many bubbles were removed. The image gives you a boring but good idea of what it looked like at this stage (you will also notice I screwed in supports to the outside frame to keep it level). Step 4 shows the concrete structure cross-section.

Spend the next 4/5 days spraying with tap water to help the concrete dry slower and harden better. Remember if it rains to cover your slab.

When the slab was a good 3 days into drying I decided to lay an outside rim of brick to hold the insulation layer. I opted for 1 brick layer at this point.

Whilst the bricks and mortar were setting I decided to get digging in the back garden for some clay. This was fun but be aware the neighbours may think that you're digging graves! I had to dig about a meter down before I hit clay (also worth noting you may not even be in an area with clay) and I pulled a good large bucket full out.

I then mixed this with tap water and another bucket of hay and mixed... this is HARD work, but eventually ended up with a sloppy mess consistent of cow muck (so way too runny) but my thinking was I would leave it to go off slightly over a few days - which it did... but it also smelt very similar to the aforementioned bovine!

A good week into this I decided to remove the outer wooden form from the concrete slab. All set and extremely hard - I'm pretty pleased with the result.

Next I layered the clay and straw mix onto the concrete base and levelled off to about 60mm.

Next come the bottles...

If you're anything like me you have probably read loads of blogs that talk about this insulation layer using bottles, clay or mud or sand... and like me you've probably struggled to have it clearly explained why?

I had no idea and I'm not sure I fully understand, even now. Every time I read a blog it said about bottles and insulation but in my mind bottles + high heat doesn't seem like a particularly good idea. But a few blogs mention about the glass and the areas in and around the glass expanding and contracting. I've also heard that the use of bottles helps to retain the heat on the base of the oven*.

In the end I decided to do a mix of bottles and broken up back plates from an old fireplace. The bottles are in the main area where the heat will stand and the fireplace bricks are around the edges to help protect any of the outer building bricks (see image).

All of these elements fill roughly the size of my 1 brick in depth.

*Permaculture Research Institute and cwolsey

When we moved into our house the garden was full of rubble so all of these tiles have been dug up from my garden and had to cut them down and trim the edges using a water based tile cutter - you'll see from the photos it's a messy process but secretly loved getting messy!

I decided to lay some fireproof screed around the edges in order to grout the tiles down (again using a fireproof grout from Vitcas). Once the tiles were down I filled the inside area with a level of screed in order to have a good surface to work with for the pizza oven floor. Again, like cement, it's worth watering the screed with tap water every day to create a slow drying period, strengthening the final finish (I did this over 3 days).

The next stage is really critical. I want an oven base that's as flat as possible in order to have a smooth area to cook on or slide the pizzas on and off. I obviously used a spirit level but i also watched a tutorial where a guy talked about using a pizza shovel/peel to slide onto the bricks as he was making it... it was a good tip and actually you get a real feel about what it will be like. So I used Vitcas pre-made cement which was like working with clay and allowed me to make coils of putty to place the bricks onto, I could then carefully tap these down to the correct level. One downside; the cement is slightly oily so actually it takes longer to set and also the weight of the bricks gradually pushed the putty down - but it was minimal.

I then did a tile trim around the outside to cover the rough edges of the brick (again using scraps from the tiles) and did a skim over all the bricks and tiles using vitcas grout. The storage heater bricks I found were fairly rough so this skim really helps to set them and fill in the edges.

N.B.: On storage heater bricks I've seen a fair few people speculating about the use of asbestos in the materials. Some say it has it in and some say it doesn't. From what I can tell; this is all speculation and not something I'm too worried about, asbestos was more than likely used around the outside of a storage heater or within the sealant rather than in the bricks themselves.

Okay, so I'm guessing by now you've probably seen loads of blogs with many different and dodgy looking brick entrances? Me too and I wasn't sure (after putting all this effort in) that I wanted to do the same.

So I decided to skip that part and just buy a pre-made version from Vitcas. The main reason I opted to do this was because I'm building a much larger metal roofed cooking area and I needed to fit a 1.5 meter 4" chimney so I didn't want to make something that was going to collapse and damage my roof. All I needed to add to the chimney was a pipe fitting which I fire cemented into the top and left to set until later. I bought my piping from The Cosy Owl through Amazon or you can contact them through Volsom.

I have no regrets and I'm really pleased with the quality. Sure it may not have rustic charm of a French barn that's about to collapse but I know for sure that... well, it wont run the risk of a falling down like a rustic French barn.

One of the things I really struggled to get my head around was the sand form for creating the dome. It's definitely worth thinking about the thickness of the clay, the area inside for cooking and the base to build on top of.

So I got my dad involved... he's a master at paper måcheté and he offered to help me out with something to guide me. His take: a space hopper covered with about 3-4mm of paper måcheté (which I think looks a bit like the death star - for all you Star Wars geeks out there). He then cut and reshaped to fit my oven door. The great thing about paper måcheté is you can fill it up with sand, cover it with your clay mix, then when you're ready to remove the sand (to start the drying process) you just burn the paper shell inside.

N.B.: My dad's an artist and illustrator - you can check out his work on instagram here

Using the paper måcheté form I filled with about 2 big bags of sand and packed down so it was rock solid. You may also notice that I attached the front of the oven first, I did this so I could cast the clay directly onto the front and not worry about cutting a hole - I completely understand people not doing this if they're constructing their own arch.

Next up: 'Puddling the clay', this is basically treading clay (best done bare foot). I used a 1 part clay and 2 parts sand ratio with some clean water mixed in. It's fun but the neighbours definitely were peaking out of their windows at me. I didn't have any tarp so I used a big bucket... I WILL be using tarp for the next layer!

A lot of the blogs say you must use quite a dry clay brick on the first layer but again I questioned this. Having studied pottery, the only advantage I could see in doing this is it will dry quicker. I've also read where people have said too wet and it will sag at the bottom, but I suggest this only happens because people are trying to make bricks whereas I wanted to 'throw the clay' meaning a quick application built up (a bit like lime mortar). The advantage; firstly you can have a lot of fun throwing clay and in the process eliminate air pockets (much the same way you would throw clay onto a potters wheel) and structurally it could be supported much quicker using the physics of the clay and the form. If you're using just a sand form coated in wet paper this may not work but my form was solid.

I used about a handful of clay roughly the size of an orange and threw the clay at the form (not too hard). Starting at the bottom and working my way around. It took about 10 minutes to do this and then I repeated the process again in the same way until the outside was roughly 100-150mm thick.

Interestingly there was no sag at the bottom and I was able to cover the whole oven in 20 minutes or less. I then went over the finished oven (with wet hands) smoothing out areas and throwing more clay into any parts I felt needed it (smoothing the clay with wet hands let me feel any inconsistencies on the surface structure).

I'm really glad I went with instinct on this. Finish was perfect and actually I was able to shape the oven without damage or sag. It took a little longer to dry (maybe 4-5 days) but I'm fine with this and actually it was just the right wetness to add the next layer.

My wife cut a cross hatch over the surface of the oven in order for the next layer to adhere better. Whilst she was doing this I puddled the hay and clay together (this time using a tarp bag). I used 2 bags of clay, 1 carrier bag of hay and a carrier bag of wood shavings.

Puddling took a while with the hay, it was tough and I needed to add water as I went to get a good consistency. After applying and smoothing out I left the clay to dry for at least a week as the hay retains moisture.

It was good to get the fire going inside the oven.

After removing the sand I was able to see that the paper måcheté form held up really well. I started with slow drying using candles but then got really inpatient and lit a small fire... one thing to note here, wet paper causes lots of smoke. I should have waited!

But all being said, over the next few days I lit several fires and was really happy with the overall shape of the clay and the fact it stood up to heat so well. I couldn't resist, but on the last firing I put sausages on a grill and had an amazing lunch.

I did a bit of research on the final layer and decided to go with a lime render coating. I did however get it wrong.

The previous clay and hay layer (second coat) shrunk after the first firing by about 10mm and before adding the lime mortar I made sure this was rehydrated with some water in order to adhere.

Although I did a fair bit of research on how to apply the lime render I still had issues with cracking. I used a 5:2 sand to Hydraulic lime render mixed with water. In hindsight I think I should have added some kind of fibre to hold it together better but decided with a smooth mortar mix.

Once applied it was easy to smooth out using a plastic card (like a loyalty or membership card). I was happy with the finish I covered it with cling film to protect it from drying out too quickly from both sun and wind. But, it did crack, not huge cracks, but I wasn't too happy with the finish.

So decided to add another layer on top of this-about 10mm thick-and this time used hay fibres to hold it together a little better. Sounds odd but I put hay into a food processor to make into little fibres, it worked okay and I was able to incorporate them into the mix but quickly discovered I had a massive hay allergy. This took a lot more working but actually it proved successful and held together much better.

After this had dried I just did a lime and water wash over the top using a paintbrush, just to give it a 'whiter' look and then finished the chimney stack through the roof. Make sure if you're doing this to use a heat proof sealant as the pipework gets extremely hot and most corrugated roofing has a plastic coating.

After making this it's really useful to put some research into how to cook a pizza. I've cooked them many times in a conventional oven but a wood fire oven is a whole different experience, so here are some tips:

1. Get a thermostat
   • Your oven needs to be about 900 degrees so it's worth knowing how hot your oven is
   • Another indication is when the top of the oven turns white
2. Shut the front door
   • I found a lot of heat escaped through the front and the fire burnt too quickly so it's worth retaining that heat with a door. At the moment I'm making one but have used a block of wood as an temporary measure
3. Burn the wood in the middle and when you're ready to cook the pizza move the wood to the side
4. Cooking straight onto the base of the oven? Get a small mop to just clean off the ash.
   N.B.: this does drop the heat down slightly
5. Make sure there's a flame
   • This is really important... no flame and base cooks but the top stay's... warm, melted but not cooked like a pizza
   • A really good tip: when the pizza is about ready, lift it up on the shovel to the top of the oven and let the flames lick the top. This uses the shape of the oven - it's a beautiful taste and finishes the pizza really well
6. Don't overload... so there's a reason Italians only put on a few ingredients... throwing a pizza into the oven is tricky (even with pizza shovel). Overload it and you'll find it tricky to turn or control
7. Lastly that brings me onto using a tray or putting it directly onto the stone
   • To start off I did it straight onto the base... it was fine but I found it difficult to cook and had a few crunchy burnt bits of wood on the first ones. At the moment i'm using trays until I can really hone my skills at using the pizza shovel. There's no shame doing this.
8. Get yourself a good dough recipe. I've made loads of bread but it's well worth investing some time into developing your pizza base. I'm still developing mine... it's good but I want to get it perfect.
   • I'll post up in a separate Instructables when I'm really happy

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Thanks for reading x