Cobbing

Last winter I read A Hand Sculpted House: A Philosophical and Practical Guide to Building a Cob Cottage, written by Ianto Evans, Linda Smiley and Michael G. Smith . I was smitten. Check out these pictures of cob homes that I found on the internet*.

There is something downright homey about a cob cottage and I decided that my yard desperately needed a cob cold frame, a cob oven and a cob garden shed…

Thankfully my husband was in agreement and so we started with a cob cold frame. I’ve used traditional cold frames in past gardening pursuits, in order to extend the season or ‘harden off’ seedlings, however I wanted an insulated cold frame to allow me to grow greens all winter long. After researching this concept more, I decided on the following specs: a base of gravel to allow for drainage so pathogens would not build up in the soil, old recycled wood for a basic structure to infill with cob, and finally an old storm door for passive solar heat gain thus allowing me to grow greens during the coldest months of the year.

Here is a brief synapses of the steps we took to build the cold frame. (See pictures below) We excavated the site roughly a foot below ground level, then layered sand and gravel to ground level in order to allow for good drainage. After this we mortared cement block (not my first choice) in place to make a foundation as the cob cannot sit directly on the ground. On top of the cement block foundation we placed the wood frame that my husband fashioned out of scrap wood.

After the structure was in place we needed to figure out how to cob. Cob is an old building method used all over the world that has recently been experiencing some popularity. It is a mix of sand, clay soil, water and straw. There is no set recipe for cob as all clay soils are different, thus much of our time was spent deciding on what ratio of clay soil to sand would make a good cob mix.

After we had the recipe worked out we enlisted the help of our three year old. The best way to mix cob is barefoot on a tarp and it was a messy good time. After thoroughly mixing the cob, the mix is formed into ball-like gobs and slapped in place on the wall. We then used sticks to ‘goob’ it all together to form a wall and proceeded slowly, with a level. As the walls grew we became more efficient in our mixing and more confident that we were actually making cob.

Site excavation, adding sand and gravel.

My helper rearranging the foundation

We used this wooden ‘tray’ to make test bricks. On the side of the wood we wrote the various cob ‘recipes’. This was extremely helpful as there is no ‘one recipe’ for making cob as all soil behaves differently. End result was a 60:40 clay to sand ratio.

The wood frame in place and ready for cobbing.

The first layer in place! Note the vents in the back wall to assist with temperature regulation.

Close up of the back wall wrapping around the wood frame.

A confession – towards the end we pulled out the power drill to help mix the cob.

Cob in place and drying.

Project complete! So far it has been excellent at regulating temperature fluctuations.

*Citations for the cob homes:

#1: http://ilovecob.com/archive/fruth-brown-cob-house

#2: http://tinyhouseblog.com/tag/ianto-evans/

#3: http://www.homedesignfind.com/green/escapees-from-mcmansion-ethos-build-tiny-cob-home/

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