if you have to little sand add sand if to little clay add clay. the organics should be removed if you can but a little wont hurt. after the cob is mixed add straw till it is well mixed in then build. if you are doing the core of the stove/bench Erica and I like to do what we call thermal cob. its just a good cob mix without straw. I would suggest you do test bricks to see if the mix is right the bricks should be about 1 inch thick by 2 inches wide by 4 inches long. dry the test bricks in the sun or if you have no sun and heat you can dry them in the oven. the batch of cob you want is the one that cracks the least. very small cracks are ok but the fewer the better. Try for a batch that will not crack at all. when you have a good batch mix all the rest of the batches to that set of proportions.
Reginald Morgandorfer wrote:I bought clay at the local art supply place. Probably not the cheapest solution but if you go and find out who their supplier is, you might be able to get a larger quantity for a more sensible price.
Otherwise make friends with someone who has heavy clay soils and get to digging!
Sand, silt, and clay make up up to 80 percent of ALL soil on earth. In places like Texas Clay makes up over half and up to 90% of some soils in many areas. Paying for clay seems ludicrous to me since it clearly makes up a huge percentage of the earth we have all around us. Here is a video about how to extract clay from earth.
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