Playing with gloop

14 05 2017

I’m often asked – and I often ask myself – why do I own three utes?  Well dear reader, I just worked it out! At very short notice, I got a text message from Matt next door that Steve could start cutting the trenches that have to be the foundations for our house’s slab on Friday afternoon, and Saturday norning if necessary to finish the job. Typically for Tasmania, the weather forecast went from fine weather to calamitous……. thunderstorms and minor flooding for the North of the island was predicted, and this fortunately did not eventuate, but as luck would have it, we in the South ended up copping some.


Ready for action

Because the trenches are too far from the embankment where I want the earth moved to, it would all need to be moved with a vehicle, so I hunted around for a small tip truck, and found one, but as usual, the locals let me down again. I sometimes wonder how they stay in business…..


So I set up all three utes like a train, and lined Caleb up to come back, hopefully with a mate, to do all the hard yakka. The mate could not make it on the day, so the pair of us worked our arses off, shoveling and 20170512_135641shoving and shuttling utes around trying to keep up with the digger. Which we largely managed to achieve…… but as luck would have it, as soon as the first ute (the 4WD one) was loaded and ready for moving, it refused to start. Luckily it has a very strong battery, and I actually managed to reverse it, with a ton of mud on the back, with the starter motor, to get it out of the way and reverse another ute in its place…. not a great start.

20170513_083021Amazingly – and very fortunately it eventually turned out – the 4WD started first kick a couple of hours later, just as the rain started….. I say fortunately, because 2WD utes don’t do gloop…!

A few months later, I discovered that this ute had the wrong spark plugs fitted.  It’s all good now…

Eventually, having finished the main trench down the front wall, we called it a day. Overnight, we got just over 6mm of rain, and in the morning, the site was really starting to look like quagmire, and the clay was getting heavier and stickier, making it largely impossible to shovel by hand. With only one ute able to get up the hill with a load (yes, it started again!), slip sliding all the way to the unloading site, it was decided that it would be more efficient, and certainly easier on us with the shovels, for Steve to move the excavator up the hill and scrape all the clay with the mud bucket off the tray….  Aah, the power of fossil fuels!20170513_091727

It was eventually all done, though where the lateral trenches came out through the edge of the main one, so sticky was the clay that a lot of earth came off the corners. The odd rock didn’t help either, and everywhere excess dirt is removed, more concrete will have to replace it, costing both me and the environment. Some things just can’t be helped, one has to deal with the situation at hand….20170513_100748

Caleb and I even had to stand in the trench to lift, mostly by hand, large clumps of sticky clay into Steve’s bucket so it could be lifted on the back of the ute and moved uphill. Let me tell you, I really look forward to the day this stage is over!

To put into perspective how bloody sticky the gloop was, I’ll leave you with a shot of the 4WD’s foot well that I will have fun cleaning up one day…. I even found the rubber pad off the brake pedal in the grass later, where it had obviously been so stuck to my boot, I pulled it off the metal pedal to get out the car! Pure luck it came off my boot right where I stepped off……20170513_110907



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…

The Cob Oven Saga, part II

29 05 2014

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

IMG_0339IMG_0340Having finally finished the brick arch entrance, we then began building the support base for the sand mould that the inner clay dome is supported by.  Without a strong support, it’s impossible to build a dome, and wet sand is what is normally used.  The only trouble is, we could not get the sand to stay vertical for the first 100mm of its rise, and I ended using scraps of zincalume sheet metal lying around to hold it up.  I was going to remove it before stacking the clay onto the mould, and thought the better of it, I reckon it can be removed along with the sand through the door when the time comes…..

One important thing to mention at this stage…….  it seems universally accepted that the height of the entrance door should be 63% of the internal height of the dome (ie, sand mould..), and that the height of the dome should be 63% of the diameter of its base.  For this particular oven, that turned out to be 400mm high, and 635mm in diameter, but if you’re going to build one too, the dictating factor will always be the height of the entrance.  To make sure we got the height right, I used a spare piece of 6mm dowel which I marked with a pencil 400mm from one end and inserted into the sand at the centre point of the oven.

Serge, whose advice on building these things is second to none, thinks that as his technique evolves the dome should be thinner than what he has been doing for the past dozen years or more.  I’ve looked at youtube videos too, and frankly, nobody does exactly the same thing, and really, as long as it works, who cares how it’s done?  As we had started to build the dome at the base some 75mm thick (which is what Serge did nine years ago on the original dome), I decided to try a hybrid method where the wall thickness decreases as one reaches the top…….  Will it work?  Watch this space……

IMG_0344The important thing to understand here is that it has to be thick enough so as not to collapse, but thin enough to dry properly to the middle of the wall.  Clay shrinks when it dries, and it will shrink even more when it will be fired; and if it shrinks unevenly, you could have a collapse on your hands.  At least, this oven, being on the southern side of the house is in total shade all day at this time of year, and even though it is unseasonally warm here for this time of year (another 28°C day today…. in May?) I’m hoping for a good result.

Serge tells me the trick is to watch for the outside to start cracking, whereupon the inner sand mould can be removed to allow the interior to dry.  patience is the word of the day, even if Glenda’s birthday is a mere 13 days away, and the Pizza Chef is chomping at the bit to fire it up and make some pizzas!

IMG_0347IMG_0349Serge also expressed concern that as the clay shrinks it might separate from the brick arch which will not shrink……  so this morning, upon uncovering the beast from the tarp that stops the heavy dew from slowing the drying process, I decided we should cover the bricks with cob, and make this cover overlap the neck of the oven in an attempt to key the oven to the arch.  it also stops the bricks from moving, which they did as we tamped the clay against them.  It’s all experimental, but there you go.

IMG_0350We made the cob mix pretty wet so that it would key into all the brick arch’s irregularities…  the bricks I’m using are pretty rough in texture, as are my cuts!  Now we wait.  it’ll be a few more days before we can finish it, the sand has to come out, and the inner dome must dry before we can cover it with cob, and then the outer render.  In the meantime, Alessandro will just have to keep making pizzas in the AGA…

Continued here……

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….