How To Set a Fence Post

Properly setting fence posts is imperative in building a straight, sturdy fence. Improperly set posts will shorten the life of your fence, cause problems during construction, and lead to problems such as heaving. By following a few simple rules, the accurate setting of posts can be achieved simply and quickly.

It is important that you have your utility companies mark any underground gas, electrical, or water lines before you begin to dig. Rupturing any of these lines while digging can be very expensive, and there is a danger of injury or death in the case of electrical and gas lines.

The first step is to mark where to dig the post holes. This is most easily done by running a string line, then measuring the increments between posts. Each spot you wish to place a post in should be marked with spray paint. Once your markings are in place, remove the string line.

Holes can be dug by hand with a shovel or post hole digger. A power auger is worthwhile if you have many holes to dig or if the soil is very hard. Post holes must be at least three feet deep. If you are building a fence higher than six feet, the hole should equal 1/3 of the distance from the bottom of the hole to the top of the fence. It is also recommended that you add a few inches to the bottom of the hole for drainage gravel.

It is best to set posts with concrete although code restrictions in your town may require the use of some other material such as course sand or crushed limestone. If you are using concrete to set your posts, you should take the time to “banjo” out the hole so that it is wider at the bottom than at the top. This will help to prevent heaving, especially in areas where there is a regular freeze/thaw cycle.

Most home centers carry bagged concrete mix. It is easy to use, just add water and mix it in a wheel barrow or bucket. This formulation may be cost prohibitive in larger projects however. You can order premixed concrete delivered to your home. Let your supplier know what it is being used for and they will mix the appropriate formulation. If available, an additive of fiberglass strands is recommended because it increases the longevity and strength of the concrete.

When setting a post, it is essential that the post be upright, in line, and squared with other posts. If it is not, the fence will not appear straight. To ensure that the posts are in line and square, use a string line stretched past the position of your end or corner posts. Align each post so that it is square to the line. Since a slightly misplaced post can move the string line, keep the post 3-1/2" from the string. A piece of 2x4 can then be used to ensure that each post is the same distance from the string, or you can measure the distance with a tape.

If you are working alone, you will need to attach temporary supports to the post before you fill the hole. If you are working with a partner, it is best to have one person align and hold the post while the other fills the hole, then add temporary supports to hold the post while the concrete sets. These supports can be as simple as two 2x4's, one for each plane. Attach them to the post with nails and extend them out to stakes driven into the ground. To ensure that posts are perfectly upright, use either a plumb-bob or a four foot spirit level to check each on two planes .

Setting times for concrete vary widely. A quick-set mix designed specifically for posts is usually hard enough for temporary supports to be removed after two hours, depending on ambient temperature and humidity. Other concrete mixes can take several hours longer. No matter what sort of concrete mix is used, it should be allowed to cure for 12 to 24 hours before further construction continues. After the concrete has set, the temporary supports can be disassembled and the lumber reused.

Some fence builders construct the fence while setting the posts, using pre-assembled panels or stringers to support the fence in one plane and temporary supports in the other. While this method may save some time and makes working with preassembled panels easier, it is not recommended. The added weight and wind resistance can cause the fence to lean.