>Continued from Part 1 below.
After lunch we got stuck in making the actual oven.
First the base was paved with fire bricks – these are what the food is baked on, so ordinary bricks don’t work, as they 1. don’t retain heat the same way and 2. would fall apart. Brick crumble – not a good addition to your diet!
Kate tapping down the fire bricks at the oven mouth
The cob walls have to be a certain minimum width for the oven to cook properly, and the inside of the oven the correct shape and size and as smooth as possible for optimum air flow and heat distribution. Kate showed us how to work out and build a sand mound of the necessary measurements from slightly damp sand. It looked rather like an old-style beehive to me:
Measurements for the oven interior
After we’d built and smoothed the mound, it was covered in wet newspaper so the cob wasn’t removed when the sand was removed:
Smoothed sand with wet newspaper layering
We then started to build the inner layer of the oven with the strawless cob, carefully pushing handfuls of it against the sand mound and into each other, layer by layer, spiralling up – but remembering to leave a gap for the oven door:
The first level of the inner layer
The inner layer almost complete
The outer, insulation layer with the straw needed to be at least four inches thick. We built the layer up in the same way, but this time we got to plonk it on much harder and slap it all together – great fun! Took me back to making mudpies in the yard as a child:
The outer layer being constructed
The door blank (a thick slab of wood) was pressed into the layers and an outline cut out with a penknife around it, so that it would fit snugly.
Any pits were then filled in and smoothed with a trowel until there was an even, pit-less dome. Using a paintbrush and water, the cob was then ‘washed’ to give a final smoothing finish. Then the scraggly edges were removed and smoothed, leaving one beautiful cob oven!
A bit of final finishing
One beautiful cob oven
The oven can then be decorated by sculpting more cob on top of the oven. We decided to do a salamander – which is; 1. a lizard, which is an earth creature, 2. a mythical fire elemental, and 3. the name of a medieval kitchen grilling tool. A pretty good pun I thought…
Nena sculpting the salamander’s back
The salamander’s head (I did that bit!)
A short collapse
When the sculpting is done, we removed the sand from the oven. This helps it dry quicker. You can also paint the oven with lime pigments when it is dry, which takes two weeks. After 1 week of good weather you can light a fire in the interior and that will help the drying. After two weeks you will be able to cook you very own pizza, bread, stew, etc in it.
And there we have it – one bread oven, ready for business:
L to R: Bren, Rozzie, Derek, Rowan, Nena, Joel and myself (wearing the famous daisy gumboots!). Lil and Ben had to leave a bit early.
Kate not only runs her excellent one day courses on how to build a pizza oven, but also 5 day courses on how to build a cob house. Kate herself lives in a lovely little 200+ year old cob cottage and is building another next to it.
Cottage under construction of Cob and Straw bale with cob rendering
I was amazed to learn from her that the earliest cob/adobe building that is still in use is a 10,000-year-old building in Jerusalem. Cob has a high thermal mass, and is ideal for houses because it keeps the interior cool in summer and hot in winter, varying only about 1°C.
It’s very stable as a building material too – cob has a compressive strength of about 5-15 tons per foot! The minimum thickness required for cob structures is 7-8” and house walls are usually about 24″ thick, but there’s no need for a framework in a cob house as it is load-bearing. You can also incorporate other techniques such as straw bale construction with it, as in the cottage above
I’ve put that down on my agenda for 2011, and am looking forward to it already.
Check out both courses and some beautiful examples of her work on:
BENZER, K. Build Your Own Earth Oven Hand Print Press, 2004, 2nd ed. ISBN 0-9679846-0-2
EVANS, I. & SMITH, M. & SMILEY, L. The Hand Sculpted House Chelsea Green Publishing Co., 2002. ISBN 1-890132-34-9. www.chelseagreen.com
WEISMANN, A & BRYCE, K. Building With Cob: A Step-by-step Guide Green Books Ltd, 2006. www.cobincornwall.com