Mixing up dry-mix concrete for fence posts.
20mm ballast, when mixed with cement, is also ideal for making dry-mix concrete which can be used to secure fence posts. Mix the ballast straight out of the bag with cement in a ratio of 7 ballast to 1 cement. Do not add any extra water. Mix well. Feed the mixture into the hole around the post a few inches at a time and ram it up using a spare piece of timber or a post hole tamper, checking as you go that the post is vertical with a level. Ram up the mixture well. The post should be firm enough to stand up on its own. The mixture will absorb moisture from the ground and set hard within a couple of days. Allow approximately 1 to 1 ½ bags of ballast per post.