How do I set a fence post so it stays put?

Fence posts fail at ground level where the timber is alternately wet and dry. Depth provides stability; drainage at the base and shedding water at the top provides longevity, and most posts are set without either.

Safety

What you'll need

• Post
• Postcrete or concrete
• Gravel
• Spade or post hole digger
• Spirit level (optional)
• Timber braces (optional)

Step by step

1. Check for services before digging.Particularly near boundaries and buildings, where cables and pipes often run. A detector, and dig the first spit carefully.
2. Dig deep enough.At least a quarter of the post's total length, ideally a third for anything tall or exposed. A 2.4m post wants around 600-750mm in the ground.
3. Make the hole wider at the bottom than the top.It resists the post being pulled upwards by frost and wind. A parallel hole is easier to dig and less stable.
4. Put 75-100mm of gravel in the base.It lets water drain away from the end grain rather than sitting against it. This single detail substantially extends post life.
5. Set the post and brace it before adding concrete.Two timber braces at right angles, checked with a level. Once the concrete goes in you cannot adjust it.
6. Use a fast-setting post mix for speed.It sets in minutes rather than days. Pour water in first, then the dry mix, following the instructions on the bag.
7. Slope the concrete away from the post at the top.So water runs off rather than collecting around the timber. A flat or dished top holds water against the post and rots it.
8. Leave it to set before hanging anything.Fast-setting mix takes an hour or two before it will take load. Ordinary concrete needs a day or more.

Tips

• Metal post spikes are quicker and adequate for light fencing on firm ground, but they are far less stable than concrete for anything exposed or tall.
• Post supports that hold the timber above ground level entirely are the most durable option, since the timber never sits in wet soil.
• Set the posts first and let them cure, then fit the panels. Trying to do both at once means adjusting posts with panels attached.

Common mistakes

• Setting the post too shallow — It works loose within a couple of years, particularly in wind. A quarter to a third of the post length in the ground is the standard.
• Setting the post directly on concrete with no drainage — Water collects around the end grain and the post rots from the bottom. Gravel in the base lets it drain.
• Leaving the concrete flat or dished at the top — It holds water against the timber at exactly the point where posts rot. Slope it away.

Questions people ask