Wednesday, March 17, 2010

Cobbing Fridays!!

For 3 Fridays in a row, Old Chimney Farm hosted "Cobbing Fridays," a collection of people gathered together to build out of the earth. Together, they built a cob bench that was built in a beautiful spot within the future food forest that will soon surround it.

What is cob? Cob is a mixture of sand, straw and clay rich soil. This material is readily available in the ground beneath our feet. It can be used to build cob benches, ovens,even houses! It can survive a fire and withstand earthquakes. It is the building material most widely used throughout the world. It has a low embodied energy, a truly "green" building material.

We built the bench foundation dry stacked with a mix of stone and brick/gravel infill. All of the material was just lying around the property. Sometimes you just have to make a few before you start to get it right, so if you don't know how to build a foundation, I encourage you to just give it a try. You'll get it. Just stagger the joints and when you hear a clunk instead of a clank, you'll know that was the right rock.

We mixed the cob at a ration of 2 parts clay soil to 1 part sand. We figured out this ratio by making a few test batches and checking for things such as cracking, brittleness, etc. A few of us worked as teams taking the batch of clay and sand and first mixing it on a tarp dry. After it was mixed we'd add water and do the cob dance, jumping around in the mud with our bare feet mixing the water into the material. After that was throughly mixed we added straw. We added as much as the mix could hold.

Now we have ourselves a good cob mix. Moist and plyable, ready to put onto the bench. We proceeded to build the bench with batch after batch of cob, kneading each new layer into the layer beneath with our thumbs. The kneading is very important because that is what gives the cob it's strength, the fact that it is one solid piece of earth. This goes on until you get the desired shape,leaving the bench rough and ready for a plaster.

We mixed plaster with a mix of sand, straw and clay, but just in different proportions to the cob. We added 2 parts sand to 1.5 parts clay (sifting the clay soil this time with a 1/2inch screen), with a medium cut straw. We spread this on as our base coat to the bench with our bare hands pushing up with the heal of our hands as well as with trowels. The Base coat went on pretty quick and easy,allowing us to move right on to the finish coat.

So one day I got a bunch of unfired clay flutes from this place downtown,100% pure clay. Great for finish plaster. You can pigment it any way you like. They had some red clay so we decided to go with that. Mixing it with sand, we applied this coat as a paste, almost painting it on to the bench and giving it color.

That's all it took, just three days, 6 people each day for 5 hours, piece of cake,right?
If anyone wants to build their own bench or has questions,just drop us a line.

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