By Dave Beetleshack
A little while back, we posted Dave's "how to" on building your own wood fired oven. Given that we are in the thick of the cold winter months (in the southern hemisphere anyway!), we thought it worth while to revisit an oldie, but a goodie - with a few updates. The oven in this post has been getting a real work out during the day while we work in the garden, and cooking our dinner in the evening while we unwind!
Why not get building yours now!
I've tried to start writing this post several times now, and deleted each attempt. Each one just seemed to me like a boring text book entry... but if I'm going to get this finished, I must now commence regardless! I do apologise if it is tedious; should you at some point throw up your hands and yell "BORING" at your screen, never fear, there are are plenty more articles out there that describe how to build one of these things. I will not be offended if you leave to find something more interesting.
When it comes down to it, a wood fire oven is really a pretty simple structure, albeit with some impressive geo-physics backing it up. They've been around since the roman times (and are hence sometimes referred to as roman ovens) and there are as many shapes and size variations as there are people roaming this blue planet. While you could just go to a hardware store and buy one for around $850, the nice thing about making your own is that you can make it however and from whatever you want (an added bonus for a thrift monger such as myself is that if the conditions where you live are suitable, it is almost as simple as digging a hole to find everything you need).
The basic principal is a chamber that you light a fire in (D'uh); the real key is the insulation properties of the materials you use (to retain heat in the oven). Ideally you want it to retain sufficent heat to get up to mid-high 400 degrees for a reasonable period of time (to allow cooking of pizzas at the peak temps and slow cooking after the fire has died). Generally, the thicker the walls, the better the insulation and longer the duration of retained heat; the trade off here is that the thicker you make the walls, the longer it takes to heat up.
I'll break-up the construction of the different components of our oven with some explanation for each, along with some photos (or "captures" as some of you seem to be fond of referring to ;-) ).
Materials: Block, brick or stone to build walls; concrete to pour footings
Although you could build the oven at ground level (which would actually provide rather good thermal properties for the base), for practicality it makes sense to set up your oven at a reasonable working height. You can do this in whatever fancy way you like - I've seen it done with timber railway sleepers, stacked stone, rammed earth - but I had a bunch of 140mm concrete blocks lying around from a previous project so I used those.
Step 1 - decide how big you want your oven, which determines how far apart you want the walls (the space between the walls provided a handy timber storage area as well). Note: I built ours against an existing brick wall so only needed two sides; you may need three...?)
Step 2 - dig some strip footings the length desired and fill them with concrete (about 400 wide x 200mm deep is probably fine)
Step 3 - lay the blocks to the height you want (remembering to make allowance for the thickness of the plinth above). You could also fill the cores of the blocks with concrete / mortar if you felt like it.
Step 4 - Quench thirst by whatever means preferred
Materials: timber to make formwork, SL52 reinforcing mesh, concrete
Once your walls are up, you'll need something to sit your oven on, AKA a plinth. It is important that the plinth / base is as insulated as the rest of the oven, otherwise you'll lose too much heat out the base. This is a failure of my oven and something I need to address with some retro-fitted insulation. The base structure of my plinth is a 75mm thick reinforced concrete slab, cast on the floor of the carport in two sections. I cast it in two sections so that I could lift them into place. I used SL52 mesh as reinforcing and bagged concrete, and 75 x 35 pine for the formwork.
Step 1 - decide on size of plinth and construct formwork to suit
Step 2 - place reinforcing steel into form and pour concrete. Finish the surface however you want it took look (broom finish, wood float, steel trowel)
Once cast and cured, the plinthes can be stripped and lifted into place on top of the walls described above.
Materials: Unwashed river sand, clay brick pavers, mortar, beer
The base of the oven is the cooking surface and as such needs to be smooth and level (particularly for cooking pizzas). For mine, I used some scavenged clay brick pavers and unwashed river sand as a bed.
Step 1 - layout the bricks as a “dry” run to suit the perimeter of the oven you want to build and mark the perimeter edge on the pavers onto the plinth.
Step 2 - Set the height of the bed by laying the perimeter course of bricks in a mortar bed - I set mine up off the concrete plinth by approx 40mm to allow a decent sand bed under the pavers for insulation (as mentioned above, this needs further work).
Step 3 - Once the perimeter is laid, fill the inside with the 40mm sand screed and start laying the pavers, checking that the joints are tight to ensure your bricks will fit the perimeter.
When complete, the base should be level with no “lips” between pavers
Step 4 - Sweep washed river sand into the joints between the pavers to prevent movement. Base complete!
Stand back and admire your handiwork so far. You’ll likely have worked up a sweat so a cold beer is also appropriate at this point in the process (preferably a golden ale of local production and procurement).
Brick Arch / Oven opening
Materials: Plywood and timber for arch support, mortar, bricks
Dry pressed solid clay bricks are best if you can get them (you can use extruded clay bricks but they are not as good).
Step 1 - Using plywood and some blocking, knock about an timber arch that you will lay the bricks on. The dimensions of this are important! Work out what you want the internal height of your oven to be; the top of the arch/opening needs to be 66% (two thirds) of the internal dome height. This will ensure the oven works effectively; any higher and the heat will escape too quickly, any lower and the fire will not get enough oxygen (fires need oxygen). Also, the width of the arch should be wide enough to get a pizza shovel through the door.
Step 2 - Place the arch in position and stack your bricks on the timber support to determine the thickness of joints required and any cutting required. Check the support arch face is plumb so that it can be used to set the line of the arch (you don’t want the arch leaning in any direction).
Step 3 - Lay the bricks using mortar (it’s easiest to buy bagged brickies mortar from the hardware shop) up and over the arch. Keep the joints as tight - tight joints mean that the bricks will be bearing on each other as much a possible giving the arch maximum strength.
Step 4 - The arch should be self supporting straight after laying (if the mortar mix was not too wet and the joints were kept tight), but to be sure, let the mortar set and then carefully remove the timber support arch.
Now you’re ready to build the main oven component.
Materials: Corrugated cardboard, packing/brickies sand, river sand (washed or unwashed), clay, water, hydrated lime, beer
* Note - for the sand, in hindsight I would definitely arrange a delivery of sand rather than buy in bagged.
Step 2 - Cut out the shape you have marked and trace around it to make a second replica. Draw a vertical line from the apex to mark half way on both pieces of cardboard. On one of the cardboard pieces, cut from the apex down the line half-way to the base. On the other, cut up the line from the base half-way to the apex. Slop the cardboard pieces together and you should have the shape of your dome laid out in quadrants.
Step 3 - Place the form against and centre on the brick arch; you should get an idea what the oven will look like. Start piling up the packing/brickies sand in the corners of the quandrant working up and out until you have pile that is in the shape of the cardboard form. Smooth over the entire dome making sure the curve is consistent and the cardboard form is just covered at all points.
Step 4 - Get a few mates to come over, lay out a tarp and start to mix the clay (40% ish) , sand (60% ish) and water - using your feet is best as it gets the job done quickly. It is also very lovely for your feet. Once the clay is mixed well, form it into bricks/logs and lay them around the sand form in stretcher bond (each brick half overlapping the ones below) until the whole lot is covered in clay - the bricks should be about 70mm thick to form the internal wall of your oven.
Step 5 - Once the clay is sufficiently dry, you can clear out the packing sand. The only way to do this is to get your head inside the oven so make sure the clay is dry enough to support itself. Keep the sand to re-use in the lime render in step 6.
At this point, repeat Step 4 until the desired wall thickness is achieved.
Step 6 - The final construction step is the rendering to further insulate and weather protect the clay. I did three layers of render and in layer used a combination of straw, lime and sand - this is optional. Mix the sand & lime in a ratio of 1 lime : 3 sand and water sufficient to work the render (don’t make it too wet). Make sure the sand you use is not too soft / fine otherwise the render will crack all over the place - the sand is in large part reinforcement / structure in the render. Wrap the clay dome in chicken wire and start rendering - keep going until the whole lot is covered.
With a passion for all things green, Dave will be sharing his journey as an (wannabe) urban farmer. A small 1/2 acre plot of sloping land and 3 wild kids won't hold him back. From planting to harvesting to preserving, Dave is our go-to guy when it comes to the garden. On a large scale, his dream is to raise awareness of the need for reconnection of local people with local food, to benefit the general health and well-being of the community as well as the earth. You can follow his journey more closely over at Blindberry Farm.