The Cob Oven Saga

25 05 2014

Nine years ago, as I finally had the roof up on this place, it struck me as a good idea to build a cob oven, and use Glenda’s ******th birthday as an excuse to have a pizza party and celebrate the progress on the house.  I had several concrete blocks left over from the build, so I quickly knocked up a plinth outside the kitchen door (still non existent at the time, as is the back verandah an old photo reveals) high enough that the oven could be easily accessible from the kitchen……


Memory Lane

My friend Serge had built several such ovens, so I asked him for his expert assistance, and he and I began building the thing.  We got as far as making the first shell around the sand mould, when the weather unleashed the wettest June on record….  it just rained and rained and rained, and the oven ended up covered with a tarp well past the birthday; to boot, everything went wrong on the weekend of Glenda’s **th.  One of the rear tyres on my car self destructed, and I only made it back to Brisbane by the skin of my teeth.  Worse, the cooling system on Glenda’s car also gave up the ghost, and we had no car to go out with to celebrate the milestone.  Luckily, a friend of Glenda’s took pity on us and saved the situation.

I had a house to build, and no shortage of other things to do, so the oven was put on the backburner.  Eventually, the tarp disintegrated, and the whole thing collapsed in an ugly heap that eventually saw native bees nesting there, and moss and weeds growing all over it…….  I have to say, I have no idea where the nine years since went, but to say the mess was a bone of contention here is the understatement of the year!

cleanupHaving an Italian Pizza Chef as a Wwoofer inspired me to rebirth the project.  Plus of course, it’s Glenda’s birthday again soon, so now I have another deadline.  No pressure.  Watching how long it took the Wwoofer to just clean the whole thing up to reach this stage reminded me of why I just ignored it.  What a job!



Serge recently built himself another oven at his place in Gympie, and gave me some tips on best ways to modify the original all cob design.  It was decided to make a brick arch doorway to the oven instead of the original clay one.  I decided to make a full size drawing of the brick layout and use it to make templates… but who says things are meant to turn out as planned?

Cutting bricks

Cutting bricks

I bought a nine inch (230mm) diamond cutting wheel for my father in law’s old AEG angle grinder only to find it could only cut about ¾ of the way through the bricks.  Undeterred, I mounted the machine in a device I bought for peanuts at a garage sale designed to turn angle grinders into metal cut off saws.  Getting the cutting angle right in a device only designed to make 90° cuts was challenging to say the least, and time consuming.  After mucking around for what seemed like hours, I finally managed to shape a brick into a wedge shape that closely resembled the template I had cut from the drawing……. only to discover once I’d finished that you really only have to be one degree out over twenty four cuts, and…….  you’re out 24°!  There went my ambition of making perfect mortarless joins like the Romans…… or was it the Mayans?  One can always dream….!

Where's the keystone?

Where’s the keystone?

Having ground the wedges again to more closely resemble reality, I then decided to do a practice

Finished Arch

Finished Arch

run using cardboard wedges as temporary ‘mortar’.  I’ve seen brickies build arches in houses, so I had a pretty good idea of what was necessary, and made an arch support from two pieces of scrap plywood; only to realise once I could see the arch ‘in the flesh’ as it were that without a proper keystone, the arch might not be stable enough to support its own weight.  So back to the grinder it was and four bricks were cut into wide keystones (I only needed three, but as luck would have it, I stuffed one up!)

I have to say, I won’t miss this dusty part of the process.  Or the noise.  But it’s done.  The arch is self supporting, and all the gaps are bogged up using some of Glenda’s ceramics clay.  Don’t know how much it’ll shrink, but the arch will be finished with an added layer of thick cob on top, and that should hold it together nicely.

Watch this space.  next week, Alessandro the wwoofer and I are going to get stuck into making cob to finish it.

Continued here….