just looked in Ussery's book he does use wood ash also DE or lime, wood ash at no more then 2 parts out of 6 or 7 any dry soil will work does not need to be sand and sift the ash and peat to remove small sticks and lg chunks of coal, although I have read coal has minerals that are good for chickens.......I use a box with 1/4 in hardware cloth to sift my peat and ash, don't forget to wear a mask