What Kind of Concrete Do You Need for Fence Posts?
If you’re installing a fence with posts in concrete (or having one installed by a fence company), you might be wondering what kind of concrete do you need for fence posts.
Let’s take a closer look at what kind of concrete is usually used for fence posts, so you can make informed choices.
How Strong Is Fence Post concrete Usually?
If you know a little about concrete, you will know that its strength is usually measured in MPa or Mega Pascals. This is a unit of measure that defines how much compressive strength concrete can be subjected to before it starts to crumble and disintegrate, and it’s usually tested in large hydraulic presses during a cube test.
However, we already know what strength concrete will be if we know the mix design of the concrete, and that’s particularly true when using ready-mixed concrete.
Compressive strength is usually measured at seven days and 28 days after the concrete is poured, but concrete can actually keep hardening for many months after it is poured, so it will keep getting stronger for some time.
The compressive strength required for fence posts is usually 10 to 15MPa, although some higher, heavier fence systems might require stronger concrete.
What Kind of Aggregate Should You Use in Fence Post Concrete?
Concrete is a complex material that can be made and mixed in many different ways, but there are always the same basic ingredients: cement, which is the component that undergoes the chemical reaction when mixed with water; sand, also known as fine aggregate, and stone or gravel, or coarse aggregate.
Coarse aggregate for concrete comes in many different types and sizes, but because fence post holes are usually fairly small, it’s a good idea to choose one that is relatively small, often between 13mm or about ½ an inch to 19mm or about ¾ inch.
Do Fence Post Footing Require Reinforcing?
One way to increase the tensile strength of concrete is to use reinforcing or rebar. Unlike concrete, steel has a very high tensile strength, and when it’s used in concrete, it can greatly improve the structural strength of a beam or slab.
However, in most cases, fence post footings are more functional than structural. They’re designed to hold fence posts in place and act as an anchor, but they usually don’t carry a lot of weight or force. That might be different if you’re talking about a very tall or heavy fence system, though, so if you have any doubt, always consult an engineer.
Should You Use Concrete Additives for Fence Posts?
Concrete is a lot more complex than most people realize, and aside from the usual stand, stone, cement, and rebar you might expect to find in your concrete mixture and design, there are also chemicals known as admixtures that you can use to improve the performance and workability of your concrete.
Some of these admixtures are designed to make concrete harden faster or improve other aspects of the concrete’s performance. While admixtures can improve the strength and performance of concrete, they’re not a required addition to your concrete mix design.
