- When installing fence on your property it is important to remember that the only support for the structure are the fence posts. And, no matter what type of fencing you use, the structure will have to bear against a substantial wind force. The most common form of fence post anchoring systems is concrete anchors. When entering the fence post into the earth, wet concrete is poured into the hole around the post. If done properly, the concrete dries and sets forming a heavy anchor into the surrounding earth. The fence post embedded in the concrete is secured by the weight of the anchor.
- In order for the concrete to adequately anchor your fence post, it must be poured and set correctly. Post holes must be dug to form an upward-facing cone shape. This shape will greatly increase the strength of the fence post and the volume of wind force your fence will be able to resist. The most common mistake when installing concrete fence post anchors is the inability to achieve the proper anchor shape. The easiest way to address this difficulty is to purchase a plastic post anchor form from your local hardware store.
- Depending upon the environment, the concrete anchor may encounter a number of stress conditions that should be considered before beginning the project. A condition that causes the greatest impact on improperly anchored posts is called "frost heave."
When water in the surrounding soil begins to freeze, it expands. This puts lateral pressure on the hardened concrete fence post anchor. If the anchor originally set in the shape of a downward facing cone, the lateral pressure will literally heave the anchor upward. This effect will drastically reduce the structural integrity of your fence. - If you live in an area that experiences high volumes of rain or snow, it is important to understand that concrete is porous by nature. Unfortunately, this characteristic means that in climates where the surrounding soil is often damp or wet, the concrete can draw moisture into itself and the encased fence post. If you are using wooden fence posts this may mean your posts will have a higher likelihood of wood rot. In order to help resist this scenario, wrap the portion of the post that will be seated in the concrete with several layers of plastic Saran Wrap. Also, you can use at least 5 inches of angular cut gravel packed tightly at the base of the anchor before pouring the concrete, this will help channel excess water away from the posts and into the surrounding soil.
- Several additional alternatives exist for anchoring fence posts into the ground. These include anchoring posts using metal spikes, anchoring with drive anchor footings or anchoring using angular cut gravel. Using metal spikes is often the easiest, though it is only appropriate if you are installing a lightweight fence with a low (2- to 4-foot height) clearance, as metal spike anchors have the least amount of stabilizing force. Drive anchor footings are typically used in national parks and in government fencing projects where maintenance and replacement will be infrequent. This strategy is typically not used with decorative fencing. While it may be less expensive than the concrete method, and it is sturdier, it will be very difficult to find a contractor willing to use this method on a residential project. Using tightly packed gravel often will produce an anchor that is similar in strength to a concrete anchor and is a method that can be done without a contractor. Unfortunately, there is a good deal more labor involved since deeper post holes are needed, and ensuring the gravel is tightly packed around the post can be a good deal of work.
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