Wood Fired Oven

December 13, 2009

Wood Fired Oven Construction

Hi guys and girls, this is my little story of how I built our wood fired oven. Before I get into the details of building  the oven I should point out that I had no real idea of what I was doing and have never actually built anything before. So please don’t make the mistake of thinking that I know what I’m writing about.

All the dimensions and construction methods came from the book “Your Brick Oven:  Building It and Baking In It” by Russell Jeavons and various websites both American and Australian.

The first step was to lay the concrete slab.  This was approximately 105mm thick and wide enough to support the besser block base that is 1600mm by 1600mm.  The bottom level of besser block was laid on a bed of mortar and made as level as possible.  The remaining two levels were dry stacked and had half inch reo drilled into the concrete slab on the corners as per photo below.  Concrete was then poured in the besser block voids.

Two columns of besser block were placed in the centre of the void to support the middle of the concrete slab that would support the oven floor.  You can see by the photo below that I have made a void on one side (the far side in this pic)  which would allow the stowage of fire wood.  To support the concrete slab on that side, I placed a 30mm by 30mm length of galvanised angle bar.

In the next photo, I simply filled the top of the besser blocks with sand to level off where the concrete sank in.  In hindsight, at this stage I should have backfilled the large void with sand gravel or insulation, but I don’t think it’s really necessary.

The floor of the concrete slab is formed by using cement fibre sheeting.  I then boxed it in, laid the half inch reo and filled up with left over chicken wire.

Once the wooden edging was removed from the slab, a line of solid clay house bricks was used to not only hide my crappy concrete work, but to also provide a solid border that would hold in place the bricks for the floor of the oven.  The bricks were laid on a bed of approx 10mm brickies sand.  The next step at this stage was to mark out the centre of the floor and then mark out the internal dimensions of the oven using a black marker and a 550mm string line.  At this point you would also want to mark out exactly where you want the door opening to face.

The dimensions for this oven are as per the book by Russell Jeavons, 1100mm inside diameter with the inside height of the dome being 550mm.  These dimensions allow for good air circulation, smoke extraction and enough room to cook 3 large pizzas at one time.

The first step is to dry lay the bottom row of bricks and lying them around the black line marked ensuring that the inner edges of the bricks join along the line.  Once you are happy with how this looks, then fill the gaps between the bricks with mortar.  For whatever cement you are using for your mortar, refer to the instructions on the packet for sand/lime/cement ratios.  Once I had the first row completed, I then constructed the archway using a plywood guide to support the bricks while the mortar set.  The archway is 540mm wide and 330mm high as per the book.  Once the archway is constructed, this allows you to fill in the gaps where the rows join the archway.

The plywood guide you see in the photo below is a quarter circle 550mm high and 550mm wide.  When the corner of this is placed on a mark in the centre of the oven, this allows you to swing it around and position each brick as you go.  I initially tried to make a mould out of wet brickies sand as used in other references, but found this in itself was an enormous project which then collapsed under its own weight when only two thirds complete.  The other benefit of using a plywood guide, it allows you to see your internal brickwork as you go.  After the first row, ensure that the face of the brick is flush against the guide filling the void at the rear of the brick with mortar.  At this point, I should point out the bricks I used were normal solid clay house bricks.  These bricks are kiln fired at around 1100 deg Celcius and are more than capable of doing the job required.  Fire bricks may be used, but cost around 3 times as much as a normal house brick.

In the photo below you can see that around the fifth row, I inserted a thermometer that I bought for $12.50 from a catering store and simply placed between 2 bricks in the wet mortar with approx 7cm clearance from the brickwork to allow for subsequent layers of insulation and mortar.

In the next photo, you can see the dome is almost complete and I am still using the plywood guide.  The job slows up at this stage as you have to allow more time for the mortar to grab as the bricks are now at quite a steep angle.

To complete the dome, I snapped one corner off the plywood guide to pull it out the doorway.  I then placed a smaller piece of plywood on a couple of bricks and a poystyrene base and moulded the shape of the dome with wet sand.  I then placed the remaining bricks in, chocking up the gaps with smaller pieces of brick and then filling the remaining gaps with a fairly wet mortar mix.  This is to allow the mortar to penetrate into all the remaining gaps without having to be forced in.  I then left this for a couple of days and then breaking apart the polystyrene and removing the support bricks and sand, leaving the dome complete.

I then rendered over the entire dome.  At this stage the oven can be used for pizzas!!  We have fired the oven to 360deg C no problems at all.  The second layer of render included cow poo to act as a binding agent for the sand and cement, preventing cracks in the finish and acting as an insulating layer.  This render was approx 20mm thick.

The insulation we laid over the oven is mineral rock fibre rated to 350 deg C.  It should be pointed out that after having the oven at well over 250 deg C, for a number of hours, it is quite comfortable to place your hand on top of the dome without burning yourself.  My wife actually likes lying on top of it on cold nights.  This layer is more for baking than cooking pizza as it will help retain the heat within the oven.  The insulation is held in place with chicken wire and galvanised nails which also give the next layer of render something to grab on to.

A few more photos and explainations to follow in the next couple of days, along with some photos of the firings and pizzas!!

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