Forest Gardening meets Deep and Personal Ecology

Fire-breathing Lion cooks biscuits

About 2003 I had a great deal of fun helping build my first cob-earth structure and oven at Convergence Gathering so when Rachel and Nick (pictured) came out from England to teach us cob earth building I was keen to see what they would do.

Well they did it in a week and on February 28, 2006 they christened Harmony's first cob oven by baking biscuits in it.

Cobbing in the Fire Bath

In this photo I'm holding the arch of cob, which until we placed more cob handfuls around the straws (see the straws in the cob gap on the right) would fall under its own weight.

Two bundles of about 12 hollow shafts of long grass growing on site and about 80cm long where overlapped at their ends to give about 130cm of straw reinforcing. A handful of cob thumbed into the overlap locked them together and formed the top of the arch. This was held steady while cob was worked in around the rest of the straw. Once all the cob was in place and anchored onto the rocks in the foreground the arch though wet, held itself in place. A weighted stick leaned against the top made sure it dried against the fire bath as closely as possible. The dark cavity is the firebox, and to this day the cob has not leaked smoke around that arch. You can see the stainless steel chimney flue at the rear. The cob has also been marvellous at slowing what is otherwise such a rapid rise in heat that fire baths are well known for being too warm. A small fire warms a bath-full of water in about 45minutes and the cob sustains the heat for about two hours, which is great for me as I love long, long baths in non-chlorinated water!

The Cob Oven gets a Home

Rachel and Nick were emphatic that a cob oven needed to have a roof so in the coming months I took my confidence in hand and built a cob-earth wall to the west of the oven – and that gave us not one but three cob structures without a roof over their heads.

The oven stayed well protected under its tarpaulins, and the cob fire bath had a corrugated iron roof, which protected it well, but the wall was not so easy to keep covered and suffered from considerable erosion in the winter.

So the following summer I added a cob earth wall to the south making the L-shape that stands today, and had considerable fun teaching many volunteers the art of cobbing.

Both of the walls, the oven, and the bath, are built on a foundation of rocks gathered on site and this led to a fascination I have for this subject to this day. A fascination that I continue to teach wherever I can.

From about half-way up all earth walls I embedded logs wrapped in No.8 fencing wire that protruded from the top of the wall and were later stapled to the roof beams locking both together very firmly indeed.

It had been my fascination to build cob-earth wall that would hold up a roof rather than closing in with cob under a roof already built. I must say that I think the latter is the much easier option and after building a free standing west wall that held the roof via its No. 8. a post was set on each side of the oven to hold a roof that protected the oven from the most frequent rain winds from the west.

Perhaps because I didn't really want even these posts holding up a roof that cob could I gave them shallow footings and the wired a foundation of rocks to them upon which I built low cob walls that locked the oven to the post on each side of it.

The south post was also covered with chicken wire and again with No.8 wire it was tied to the cob. So it is the south cob that is really holding it steady.

With these more posts in place on the east side of the oven the roof was extended to completely protect it from the misty easterly winds we occasionally get.


This roof and the earth walls are low to the south and west, high at the central ridge over the oven, and high to the east and north. This means the east half of the roof has a lovely curve to it that can be seen in the photo above.

We named the earth building Danaa and gave her large windows and vertical weatherboards of local macrocarpa treated with natural oils containing traces of the safe anti-fungal copper-8-quinolinate as its preservative. These walls are lined with a variety of insulators. In some places wool jerseys stapled up to stop cold outside air sneaking in around them. In others a clay slurry was mixed 1:9 with untreated wood-shavings to make a type of papercrete in which the curly wood shavings were kept as fluffy as possible, with a minimum of mixing, to minimise shrinkage and maximise the loft and the insulating effect of the air pockets therein. Once this dried it shrunk about 2% and the gaps were closed with natural wood batting.

The objects in the foreground of Danaa are black 200litre and white 1000 litre containers destined to hold water off her roof.

Annual rainfall is about 1000mm and the eaves are 600 – 900mm to protect her from the rain from the west and south. The walls do get wet, but I find that as long as the rain has little driving force behind it the wall does not erode, and then dries out again.

Being in a cloud forest there are many damp and wet days but the cob keeps sufficiently dry and its thermal mass is doing a great job releasing heat back to us snuggled inside in winter.

As Danna is built in a hollow her foundation rocks get wet feet, and the cob we packed between them also gets wet at times then dries again. Drainage gravel and draincoil has been placed on her west side, where the drive is above her floor level and this carries water to a drainage sump near her south-east corner. Above this sump a pond collects excess runoff and its overflow takes the water about 20m away, downhill.

Before all the pond was operational the sump system handled 40cm (400mm) of rain in 24 hours with no noticeable change in foundations.

They always say give cob a good hat and dry feet, and I strongly recommend you do this where you can, but Danaa shows us, that cob, like timber, is tolerant of getting wet temporarily as long as it does no get so wet it slumps under its own weight.

At this stage we have only laid a fine gravel floor of crusher dust, as we know this breathes and dries out again from the top as well as from below. When systems are in place to completely carry away all rain-water (not needed by the tanks) we intend to give her earth floors.

Contact us soon to learn cob earth building with natural eco-friendly materials as eventually we will have all the cob-fire baths, cob walls, cob-stoves, and other cob structures that we need. In the meantime you can learn any of those by subscribing to our free quarterly Harmony e-zine to see when our next workshops are: Subscribe Now.

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Love,

David

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