HOW TO INSTALL A FENCE POST
Wooden fence posts are more vulnerable and fragile than metal. Spend some extra time and money on durable lumber and a well-drained installation, or that beautiful aesthetic will rot in a few years. Tamped soil on a base of gravel is enough to secure most posts, but consider concrete for soft soils.
Setting the Post in Soil or Gravel
Try this method if you have dense soil. You can install your posts directly into the soil as long as it's dense and has good drainage. The installation is more labor-intensive and a bit less stable than concrete, but also cheaper and (often) more decay-resistant.
Due to additional strain, gate posts work better when installed in concrete.
Choose a durable fence post. Follow local advice if possible, since climate and availability will affect this decision. Unless you live in a desert, it pays to choose durable lumber, which comes in two varieties:
Posts made entirely from durable heartwood. Western juniper, black locust, and Osage-orange are excellent choices. Pacific yew, redwood, and most cedar and white oak species can last 20+ years in most conditions.
Pressure-treated wood with about 1 inch (2.5cm) sapwood surrounding a core of heartwood. Aspen, ponderosa pine, lodgepole pine, and Douglas fir are suitable examples. Buy this from a trusted source to avoid poorly treated wood.
Note — All lumber should be labeled as suitable for ground contact. Not all pressure-treated wood is intended for burial.
Prep the wood against moisture (optional). The sawn-off ends of the fence post are vulnerable to moisture. Consider these precautions if you live in a damp climate:
Bevel the top of the fence post to a 45º angle to encourage rain runoff, or plan on installing a post cap.
Treat the two ends with a non-water-based, brush-on wood preservative, such as copper naphthenate. Wood preservatives are toxic, so follow safety recommendations on the label. Apply multiple coats of the copper naphthenate and make sure to let it dry for 24 hours after each application.
Dig the hole. As a general rule, an 8 foot post needs to be placed so that two feet of it are in the ground. If you plan to anchor the post in soil, the hole diameter should be as close to the fence post size as possible. If you plan to anchor the post in gravel, dig a bit wider — roughly 8 inches (20cm) across for a standard 4x4 post.
Use a post hole digger to dig a straight-walled hole. If the soil is hard, cut through the sod with a shovel and/or let water soak into the dirt.
Keep some dirt (or dirt mixed with gravel) nearby to backfill the hole.
Drop gravel into the hole. A couple inches (few centimeters) of pea gravel or crushed stone improves soil drainage. Tamp it down well. This is especially important if your soil has poor drainage.
You can use a wooden stick or broken wood tool handle as a tamping bar, or a piece of scrap lumber.
Position the post in the hole. Center the post in the hole, and get it level and in line with the other posts. An assistant will be useful to hold this in place during installation. However, if you are going to yourself have some 1"x 4"x 4' or longer material available. Then, drive wooden stakes into the ground on two sides and attach them with screws to the 1"x 4" to brace for “plumbing" (vertical level).
Make sure that you measure the distance between your posts to ensure that the top and bottom rails will fit.
Fill the hole with tamped crushed stone or soil. Crushed stone offers better drainage than soil, and may improve stability as well if well tamped and installed in dense soil. Whether using crushed stone or ordinary soil, shovel it in 3–5 inches (7.5–12.5cm) at a time, tamping well after each batch. Repeat until the hole is filled.
Before each tamping, hold a level against the post and adjust until level.
If you'd like to plant grass at the base of the post, use soil for the last couple inches (several cm), not gravel.
Finish with a small hillock. Build up the soil at the base of the pole to make a small "hill" sloping away from the post in all directions. The spot where the post leaves the ground is the most common location for rot. Good drainage here is extremely important.
Prepare your fence posts. All fence posts should be made from durable lumber labeled for ground contact. For more information on selecting and prepping your fence posts, see the method above.
Dig a wide hole. A typical 4x4 fence post requires a concrete sleeve about 12 inches (30cm) across. Plan to bury ⅓ of the post, then allow a few inches (several cm) for the base beneath it. A large post hole digger or post driver will make this job much easier.
Power tools can be dangerous if the soil is rocky. You may need to use a clamshell digger instead, plus a long digging bar to lever out rocks.
The width of the hole should be consistent the whole way down, not cone shaped.
Add a few inches of gravel. A base of gravel or crushed stone will greatly improve drainage. Pour 4 to 6 inches (10 to 15cm) into the hole and tamp it level.
Brace the post. Position the post in the center of the hole, using a level to guide you to a vertical position. To hold the post in place, drop two stakes into the soil near two adjacent sides of the post. Nail or screw scrap lumber between the stake and the post. Don't pound the nails or screw the screws all the way into the post, so you can easily remove them later.
Repeat for each post hole. Dig every post hole and brace each post so you can pour the concrete all at once. Use a string between corner posts to ensure that all fence posts are in line with each other.
Add more gravel. Another layer of tamped gravel will further improve drainage.
Mix your concrete. Put on safety glasses and waterproof gloves. Pour a full bag of concrete mix (or as much as you can transport) into your wheelbarrow and mix in about 90% of the recommended water according to the label. Mix for a few minutes to check the final consistency, then slowly add more water until the concrete feels like paste.
To save effort, you can rent a portable concrete mixer or the services of a concrete truck.
To save money, make your own concrete mix: 1 part Portland cement, 2 parts sand, and 3 parts coarse gravel, by volume.
Some fast-setting concrete mixes can be poured in dry, then mixed with water in the hole. These mixes tend to be weaker and more expensive, so speed comes at a high price.
Be careful not to make the concrete too runny. Add the water in small increments until the concrete comes off of the shovel easily.
Fill the hole with concrete. Shovel concrete into the hole up to soil level. Work quickly enough to use each batch of concrete before it hardens. Take care not to splash cement onto the post.
Trowel the concrete into a slope shape. Smoothly cap off the top of the cement with a trowel, grading it outwards from the post. Aim for a slope roughly ½ inch (1.25cm) above ground level, dropping to about 1 inch (2.5cm) below ground level. This pitch will allow the water to flow off the post, preventing pools of water that promote decay.
Allow at least three days for the concrete to cure. Give the concrete some time to dry and harden before building the fence or putting any weight on the post.
Seal the gap between post and concrete. Once the initial curing is complete, seal the gap around the base of the fence post. This gap will widen with natural expansion and frost, allowing water to pool here and cause rot. Seal it with a sealant that bonds to concrete and wood, such as some silicone sealants or exterior acrylic latex caulk.
Setting the post in concrete
Set posts in concrete when stability is extra important. Concrete may be necessary if you are installing a fence in sandy soil, or in very soft, muddy soil. It's also a good idea when installing gate posts to provide extra stability. The main downside to concrete is its ability to trap water around the post. This can reduce the lifespan of the post by many years. The installation described here avoids this problem with a gravel base and an open-bottomed concrete sleeve.