Preparing Cob Before any Cobbing begins, the first thing to do is test the soil (the jar test is to: fill half a jar with available sub-soil, fill to the top with water, agitate, and let settle completely). You want at least 25% clay, which will be the top layer. Behind our new tests, Shaylagh is demonstrating the salvage of previous cob test bricks (that’s a hammer in hrr hand.)  When MIxing a Cob Batch: you first sift out the largest of the rocks, toss dry with 25% clay, make a hole and fill it with water, toss again, homogenize it: (dance about smushing it with your feet), add a light layer of straw, smush it again. Then, with the tarp: roll it into a burrito, smush it, repeat. Natural Building: Abroad Tuesday, January 22, 2008 Test Bricks to demonstrate varying amounts of clay, dirt, (long) straw, and water; these are the ingredients of Cob.