Start by forming your rock shapes , using whatever materials you have available – either crumpled newspaper or paper , cardboard or Styrofoam . You can use a couple of real rocks as references . Cover the form with thin wire mesh using pliers if needed and wearing gloves so you don ’ t injure yourself . Next , mix your concrete by combining 3 parts sand to 1 part PPC cement , blending thoroughly before you add the water . You can also add your concrete pigment here if you like . Slowly add water and mix well to a thick peanut butter consistency . Use a trowel or your gloved hands to apply the cement mix over the wired shape , covering everything with about 4cm of concrete , a bit at a time .