The Cob Oven saga revisited……

4 04 2017

Sometimes, life’s twists and turns really surprise me…  A few days after his arrival, I was showing my Sicilian wwoofer pictures of Mon Abri, and specifically the cob oven another Italian wwoofer and I built there, almost three years ago now…… To my amazement, Vincent enthusiastically exclaimed he wanted to build one here too! Now, I had planned to build one, but where the house will be built, and not until it was built…… Discussing it further with Glenda, however, encouraged me to take the bull by the horns and try again…

I did say at the time that I was looking forward to putting the gained experience into building another slightly larger one in Tasmania when we finally get there…. just not this soon. My last effort was built on a one metre square block base, and this was the limiting factor for its size. It was adequate, but a slightly larger size would have been better. So what to build the base with for this one?

Digging up the house site revealed dozens of large to very large Dolerite floaters, the rock that gives the local clay its characteristic ochre colour. Of course they are all at the house site, a good 350 metres from where the new oven would go near the shed. And I needed sand, and bricks, and……… loads of hard work.  Good thing Vincent is young and fit and energetic… it was after all his idea…!

20170326_143117It was decided to build a 1.2m diameter base with rocks from the house site. Vincent and I managed to lift most of them onto the ute, but two of them were totally out of the question, with one I now realise that must have weighed close on 300kg…! They were chained up, and dragged with the trusty 4WD, very slowly in low range first gear. The biggest of the two was actually shaking the car as it was dragged along, and as it turned out to be the second big rock, it had to be lifted on top of the first one….

We tried levering it with crowbars and ramps, to no avail. It was one big heavy sucker..! Then I came up with the idea that if we could get it at least upright, we might be able to push it atop the first one with the ute’s towbar by reversing against it. trouble was, the 2WD was just wheel spinning, while the 4WD’s towbar was too high and just slipped above the rock, even lifting the two rear wheels clean off the ground…. until I came up with the idea of removing the tongue off the car, and putting it back in upside down!

To Vincent’s amazement, it worked…. he had given up all hope, I could tell. One good 20170328_101515thing about getting older is that you’ve solved lots of problems over your life, and this was just another problem solving issue…… I told Vincent that if the Egyptians could build pyramids, we could build a pizza oven base!

As you can see from the pics, these stones are very round, and not exactly ideal for building something that should resemble a dry wall. That we managed to get as good a result as we did was actually pretty amazing. The top wasn’t level of course, so it was capped with a concrete wedge platform, that also held all the rocks on top together. I don’t think they’re going anywhere soon…..

Related image

Steve Harrison’s Bourry Box

While all this was going on, I’d been searching for bricks, and even found ‘free’ ones in Geeveston on Gumtree. But the woman getting rid of her bricks gave me the run around re picking them up for days, and while searching for more, I actually hit the jackpot, finding 600 refractory bricks for $1.50 each. I wasn’t keen on spending that much money, but I had seen brand new fire bricks in Hobart for $6.95 each, and as we are planning to build Glenda a Bourry Box wood fired kiln in the future that will require way more than 600 bricks, we decided to not look a gift horse in the mouth, and bought them.

When you load things like bricks, one or two or three at a time on a ute, you don’t really think about the weight of it all…. I assumed they weighed in at maybe 2kg each, so 600 would be under the vehicle’s load limit of 1.3 tonnes. As it was, there weren’t 600 there, only 530. As we drove off, the car was making horrible scraping sounds that made me think “oops….. maybe we overdid it?” I hadn’t checked the tyre pressures before loading, which is something I normally always do… the mudflaps were scraping on the road, and the tyres we bulging ominously. I drove the 10km to Huonville very slowly, and at the first garage put a pressure gauge on the tyres, only to discover they were not that far 20170330_183738down; even at the maximum recommended 65psi, they were still bulging. Feeling really bad about this didn’t help either it turns out…. so we just kept going, covering the next 25km home, very slowly, without blowing a tyre, which was my greatest concern.

When we got home, I weighed one brick, and it turned out to be 3.5kg……. Ute one had just carried 1.8 tonnes of bricks 35km! Tough old thing is all I can say. And I think we were lucky too…..

I then basically went about rebuilding the last oven, only with a base 700mm in diameter20170402_134034 instead of 600. It doesn’t sound like much difference, but never forget volumes are in dimensions cubed, and even 10% bigger equals 33% larger volume, which pretty well means 33% more of everything, like clay and sand! Miraculously, just enough of the bricks I bought had already been shaped as wedges; they weren’t perfectly sized, but they would do, and I could skip the ugly brick cutting exercise except for the three keystones.

One thing I did differently this time was cementing the bricks together rather than use cob. Using cob made the last arch way too wobbly, cement made it stiff as a Roman arch.

20170403_081107Vincent, being the typical young, enthusiastic, and impatient young man he was assured me when we started we could finish the whole thing before he left……. I couldn’t stop laughing! The last one took me nine years I reminded him, and we’ve already lost two days waiting for free bricks. Just picking up the fire bricks took half a day, and a couple of hours to unload them… Nothing ever goes according to plan, there’s no need to get impatient over this….

But you have to give it to him, on his last day, when he was catching the 10 o’clock bus to Hobart, he got up at 6AM to help me make the sand mould. We even used up what cob was left to reach one third the way up said mould. At 9AM, he quit, and got himself ready for the rest of his life, but he left having learned quite a bit more than he had anticipated I think. I just love teaching young people these skills…..

So far so good, the first layer of cob is on, and cracking as it should in readiness for keying in the second layer. We’re supposed to have a dry week now, and if all things go well, I may even have it finished before my appointment with the digger that will excavate the house footings on Easter Saturday….


So far so good……..