There is almost no difference between cob and adobe and rammed-earth walls. They are all made from the same materials, clay, sand and straw. The only difference between them is how they stacked together to build a wall. Adobe is dried into individual bricks, then stacked and mortared with the same material that the bricks are made from. Cob is sculpted while still wet right into the shape of the wall. Rammed earth is the same as cob, except that wooden forms are used to keep the size of the walls exact.