Fence Posts: Concrete, Timber or Metal and How They Are Fixed

The posts are what a fence stands or falls on. Panels and boards can be replaced fairly easily, but a weak or poorly set post leads to leaning, rattling and eventually collapse in the first strong winds. Most fence failures we are asked to look at start at ground level, not in the panels.

This article compares concrete, timber and metal posts, explains the common fixing methods, and covers the practical details that make the difference: depth, mix, drainage at the base and what to do on slopes or soft ground.

Timber, concrete and metal posts compared

Timber posts are the most common choice and suit most closeboard and panel fences. Pressure-treated posts last far longer than untreated ones, though any timber that sits in damp ground will eventually decay at the base. Concrete posts do not rot and are very stiff, which makes them popular with gravel boards and heavier fences, but they are heavy to handle and slotted designs limit the panel options.

Metal posts, usually galvanised or powder-coated steel, are slim and strong and resist rot entirely. They are often used with composite fencing, for gates and where a very neat finish is wanted. Each material has different fixing requirements, so the right choice depends on the fence type and the ground. It is common to see a mix on one boundary, such as concrete line posts with timber gateposts, where each material is used for what it does well.

• Timber: easy to cut and adapt on site, but the buried section is the weak point.
• Concrete: does not rot and holds its line, though heavy and less forgiving to adjust.
• Metal: slim, strong and rot-free, but needs a suitable base and compatible fence system.
• Whatever the material, matching posts to the fence weight and exposure matters more than the material alone.

Concreting in: wet or dry mix

The traditional method is to dig a hole, stand the post in it and fill around the base with concrete. Concrete gives a rigid anchor that resists the sideways load from wind on the panels. A wet mix flows easily around the post and into corners of the hole, while a dry mix is poured in dry and takes up water from the surrounding ground, which is quicker but depends on the soil holding enough moisture.

Whichever is used, the post needs to be held plumb and braced while the concrete sets, and the concrete should be shaped to slope away from the post at the surface. That shedding of water matters because water that sits in a ring around the timber speeds up rot.

How deep should a post go?

As a rule of thumb, a good proportion of the post length should be below ground, and taller or solid fences need deeper holes than low or open ones. We do not rely on a single number, because the right depth depends on fence height, wind exposure and how firm the ground is. A tall, solid screen in an open garden needs a lot more anchorage than a low picket fence in a sheltered border.

Deeper is not automatically better if the hole is too narrow, so the width of the hole and the thickness of concrete around the post count as well. Skimping on either makes the post vulnerable to leaning. Posts at corners and ends of runs carry more load than those in the middle, because they are pulled from one side only, so they deserve the most generous holes and the most careful bracing.

Metal spurs, bolt-down plates and where they suit

Where the ground is hard, full of roots or sitting on concrete, digging deep holes is not always practical. Metal spurs are driven or concreted into the ground and the timber post is bolted to the exposed part, keeping the wood clear of damp soil. The post can be replaced later without digging out the whole concrete block.

Bolt-down plates fix a post to a patio, slab or existing concrete base using anchor bolts. They are useful for fences beside a paved area, but they depend on the base being thick and sound enough to carry the load. A solid fence on a thin or cracked slab is likely to move.

Rot, drainage and gravel boards

Rot starts where timber meets the ground, because that is where moisture, oxygen and fungi are all present. Reducing contact with soil and letting water drain away is the most effective defence. A bed of free-draining stone at the base of a hole can help in heavy ground, and concrete finished with a slight fall keeps water moving off the post.

Gravel boards, a board or concrete strip along the base of the fence, keep the bottom of the panels or boards out of damp soil. They cost far less to replace than a whole panel, and they also help hold back soil on borders. Where a border is raised against the fence, a concrete gravel board is usually the more durable option, since timber in constant contact with wet soil will decay in the end.

• Keep timber panels and boards clear of soil, borders and mulch.
• Shape the concrete top so water runs away from the post.
• Replace a damaged gravel board before moisture spreads to the main panel.
• Treat any cut ends of timber with preservative before installation.

Gateposts, slopes and difficult ground

Gateposts carry the weight of a swinging gate and are knocked and pulled every time it is used, so they need to be thicker, set deeper and anchored in more concrete than ordinary line posts. A gate on weak posts will drop on its latch side and drag, however good the gate itself is.

On slopes, posts must stay vertical even though the ground tilts, and panels either step down in stages or follow the slope if the fence is boards on rails. Soft ground, high water tables, tree roots and old foundations all affect how and where posts can be set. In low-lying gardens near the River Severn, wet ground is worth mentioning at the site visit. Old foundations, buried services and drains also need to be located before any hole is dug, so tell us about anything you know is underneath.

When to replace and what a site visit covers

A post that rocks at the base or crumbles when probed with a screwdriver has done its job. Replacing the failed post and the nearest gravel board is often enough, provided the rest of the fence is sound. If several posts have gone, a section or run may be worth renewing.

During a free site visit we look at the ground, the line, the slope and the fence you have, and handle the groundwork and fixing ourselves.