Wheoh: projects in the Warrumbungles: 'oven base' 26th September - 8th November 2013

Definitely in heaven - waking to abundance: birdsong, nature's resilience and the joy of difficult and challenging projects. Four projects on the go at the moment: composting toilet - begun before the fire, a vegetable garden - starting with a beautiful blacksmith made gate, the workshop - temporarily delayed by the need for some re-engineering of frames, and the construction of a wood fired oven.

The oven is slightly more than a whim. After an inspirational day earlier in the year at Ross Wilkinson's wonderful bush hut where he made delicious wood fired pizza in his bush-stone oven, it's obvious that an oven is an essential piece of infrastructure. Recent hot weather and fires in the Blue Mountains raise the possibility of a very hot summer with complete fire bans, an oven provides an enclosed source of hot water (for showers) and the ability to bake (useful for dietary variety). The process of deciding where to put the oven has made me think more about the location of a house and how it would work. But there were too many options including the site of my camp fire. It needed to be gathering point without blocking anything. In the end, I took a leaf out of Hoddle's book and ran a north south string-line right through the site (Hoddle Street). Instantly things began to fall into place. Time will show if this was a correct approach.

Before the fire I'd laid foundations for an oven/bathhouse near the tower. This includes the composting toilets (to be the subject of another post). I had in mind a stone building with a cross-groined vaulted ceiling. The base of this oven seemed like an ideal place to try to work out how to build vaulting.

In case anyone is considering building an oven, I referred to an Earth Garden (2007) collection of Victorian oven stories called Backyard Ovens and the Coonabarabran Library had Russell Jeavons' book Your Brick Oven (2004). Both were helpful with principles and materials. But as with all construction my approach was pretty much to make it up as it evolved. To make a start, I milled some timber formwork and poured a 250mm thick slab 1600mm x 1600mm (100mm larger than the 150mm recommended by Jeavons. At this point, Julien Bianchi kindly sent me Pompeii Oven Plans Version 2.0 [PDF 7.2MB] - a more detailed and authoritative text.

Bricks for the actual oven are hard to find in Coonabarabran. In order to buy some commons for the lining I drove east for an hour to Gunnedah where there is one of the last remaining family owned brickworks, Namoi Bricks. They generously gave me a pile of broken bricks. Then a dear friend in Coonabarabran offered me some large fire bricks for the floor of the oven. For the vaulted base I'd piled up half bricks in 1975 from the remains of a house built around 1910 (destroyed by bushfire) up near the spring (what-comes-to hand).

Unlike the workshop wall this project needed smaller field stones (not large in-ground stones). I gathered 3 loads with the Hilux. Because I wanted convergent arches. Palladio is always useful for inspiration on proportions. Palladio consistently delineates a foundation zone around his buildings. Where there are entrance arches, the foundation zone usually has a ratio of around 2:7 of the arch height and columns are about half width of the arch opening.

The concrete footing of 1600mm was stepped in from the foundation by about 50mm this meant an arch width of about 750mm. There was a cast iron wheel in the junk pile with a diameter of 680mm (close enough). By way of testing the idea it seemed like a good idea to make the rear wall (where the shower is to go) solid but with the imprint on an arch using the wheel as formwork.

It's curious that Vetruvius (Ten Books on Architecture - 100BC) makes no mention of how to build cross-groined vaults. Especially as the Romans pioneered the construction of two or more intersecting barrel vaults - but maybe that was in the later years. The medieval builders invented rib vaulting but the complexity of how they formed these up and worked out the manifold surface angles is quite mind numbing. No wonder the Masons became a guild of secret knowledge holders.

Talking over the problem in town (to anyone who would listen), I naively suggested to the chainsaw shop proprietor (whom is knowledgeable about everything) that perhaps I should try to become a junior Mason so that I could get hold of some secret knowledge about the practicalities of cross-groined vaulting. Revealing his metaphorical apron, he enthusiastically launched into a cautionary lecture about how Masonry was not about actual building at all but about improving 'good' people as if they were constructions.

On the way back home it felt like the best approach was to mill some more timber and start making round formwork. But just as I arrived, I spotted two of my old, burnt out fuel drums and realised they were nearly the right diameter (600mm). By wrapping them in old corrugated iron and then some flat iron from the roof of the tower, they would be close enough to the width of the wheel.

Covering the form with half bricks seemed too easy and I suspect the construction would be improved by some form of interlocking pattern of overlap. I tried different patterns on each arch. After building up the corners and installing some plumbing for the shower there was a moment of truth was when the forms were removed. Remarkably nothing collapsed!

So, rough as it is, that's the base almost completed in a mere 3 weeks. I'll need to pretty it up later with some judicious pointing. If you are interested, there is also a 3 minute video of the making of the oven base. Next step is the oven dome...

The seasons are passing and the Darling Pea has now faded. It's being replaced by varieties of yellow daisies and the beautiful, slender, shy nodding chocolate lilies (they smell of chocolate). The kangaroos are now coming in closer and most of the birds are using the birdbath. Fortunately the oven site has been shaded in the middle of the day. It's become necessary to take shelter from the sun from midday until about 3:30pm. A nice time for reading and thinking...