The Cob Oven Saga, part III

8 06 2014

This is a continuation of The Cob Oven Saga started a few days ago……

First cracks

First cracks

After a couple of days of dry weather (unlike nine years ago!), cracks began to appear on the outer surface of the inner clay/sand dome we built over the sand mould, telling us the time to remove the sand had finally come.  All that sand will now be used in the cob mix we will have to make for the outer shells  The cracks are nothing to worry about, because as you tamp the new wet cob on the outside you should largely fill those cracks, and that helps the two layers actually key together and eventually bond.  That’s the theory, and I’m sticking to it.

Sand removal

Sand removal

The amount of sand Alessandro removed was rather more than we remembered, as a 90 litre plastic rubbish bin was almost filled.  At first, a trowel was used to scrape the now remarkably compacted sand out, but in the end we used a brush to dislodge what was left to make sure we did not remove any clay.

The piece of metal sheeting we used to prop up the bottom of the sand mould easily came out through the door as well.  Some sand refused to come out, stuck to the top of the dome, but I figured it would soon enough fall down as the clay started drying, and to give it a little hurry along, I decided to light a candle in the middle of the oven.  A remarkable amount of heat comes off a candle, especially when it’s in an enclosed space like a cob oven.

A few days later – one has to be patient when building one of these – there were enough largish cracks appearing that we decided to build the first cob layer over the inner shell.  We did this with my old cement mixer I acquired from my friend Richard many years ago.  Having been left in the weather, it looked like a wreck already when I picked it up from his brother’s place way back in 2004… I even wondered at the time whether it was worth towing it all the way from Brisbane to Cooran, but when I plugged it in after lubricating all its gears, it seemed to work well enough.  I too left it in the weather for several years, and then gave it away to my mate Doug who used it when building his shed and house, who also left it outside.  So when the thought of using it again for this job came to me, I rang Doug to ask him if it still worked…. and it did!  When I went to pick it up, it even still looked just like the day I first set eyes on it.  Still a wreck!  I bet they don’t make them like this anymore….

First cob layer

First cob layer

By day’s end, the whole oven was covered in cob, and starting to look like the real thing….  quite handsome really.  After a couple of more days, I decided to light a small fire in it to speed up the drying.  Nothing too big and hot, just more substantial than mere candles.


Third cob layer

More cracks appeared on the outer surface, and more cob was added, especially on top where most of the heat escapes….

Bigger fires have now been lit, as you can see by the blackened keystone due to the escaping smoke created when first lighting the fire.  I’m not sure if the smoky starts are caused by sub standard firewood or just the fact the fire is lit in an enclosed area… but I was surprised at how much smoke billowed out of it.  I then made a door with the bit of plywood I used to support the brick arch at the onset.  The handle is made of a cut off piece of broom handle, and the insulation on the inside of the door is left over from making Glenda’s Raku kiln.  Having used the door now, I think I might have to add another layer of fibre board over the insulation to stop it ‘fluffing off’, something I wasn’t expecting it to do as nothing of the kind occurred with the kiln.

Door in profile

Door in profile


First firing

The good news is it will be ready in time for Glenda’s birthday, nine years late perhaps, but all good things are worth waiting for.  Once the cob is completely dry, which may take a few more firings, a layer of waterproof cement render will be added to ensure it will never collapse again!

I’m thinking of adding a wrought iron shelf to the front of the plinth, and maybe some nice hooks to hang hardware from; and Glenda is speaking of mosaics on the front to cover ‘the ugly concrete blocks’.. so who knows exactly how beautiful a work of art it is yet to become! One thing’s for sure, when it’s too hot to run the AGA, this little beauty will be lit for far more uses than pizzas…




3 responses

8 06 2014
Linda Cockburn

Looks fantastic! You can build your skills… and us one – when you both get here!

8 06 2014
Florence nee Fedup

When I lived in Guildford, my Italian next door neighbour had a outside bread oven from which beautiful smells used to arise throughout the years. I always welcome the bread, and yes tomato sauce in beer bottle that were handed over the fence. I envy you so.

9 06 2014

Wow! I look forward to seeing it with my own eyes one day soon 🙂

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