The grog also provides strength if you are building larger pieces.
Earthenware clay is the best clay for handbuilding pottery because of its strength and plasticity. Other clays, like porcelain, are not recommended for beginning handbuilding because they are stiff and not as easy to form. You can also use grogged clay, which contains a high amount of alumina and silica, reducing the shrinkage and protecting your piece from cracking when firing. The grog also provides strength if you are building larger pieces.