Fence Repair and Replacing Posts: How to Fix a Failed Post Without Removing the Whole Fence

Summary

Post replacement is the most common fencing repair call. Timber posts fail at ground level — the junction between concrete and timber is a moisture trap where rot begins, typically within 8–15 years depending on the original treatment standard. The post above this point is often perfectly sound; the below-ground section has decayed.

The efficient repair method depends on whether the fence above the post is worth preserving. If the fence itself is in good condition (boards sound, arris rails intact), a concrete repair spur allows the post to be fixed without dismantling anything above ground level. If the fence is old or damaged, it is often more economical to pull the whole section and rebuild.

Repair spurs are a practical solution but they have limits: they work on timber posts where the above-ground section is structurally sound; they do not suit very exposed positions where the spur's concrete mass may be insufficient; and the resulting repair is visually distinct (two concrete posts side by side, or a metal channel spur next to a timber post). Setting expectations with the client about the aesthetics of a spur repair before starting is important.

Key Facts

• Concrete repair spur — precast concrete post (typically 600–750 mm long) with bolt holes or U-channel; concreted alongside the failed post; timber bolted to spur above ground
• Steel repair spur — galvanised steel channel spur with bolt-through fixing; lighter and less visually intrusive than concrete; equivalent structural performance
• Spur length — minimum 600 mm in ground for standard repairs; 750 mm for exposed sites; the spur must resist the same overturning moment as a full-depth post
• Bolt fixings — M10 or M12 galvanised coach bolts with washers; minimum 2 bolts per spur, spaced 200–300 mm apart; drill through the timber and spur channel
• Rotted post diagnosis — push firmly at head height; a post that wobbles significantly is failing; drive a bradawl into the post at ground level — if it sinks in easily, the timber is rotten throughout; if firm, only the below-ground section has failed and a spur repair is viable
• Break-out tools — cold chisel and club hammer for concrete around existing post; bar and chain for pulling rotten post stubs; post puller hire available for stubborn concrete-encased stubs
• New post concrete cure — C20 or Postcrete; 48 hours before transferring fence load to new post
• Panel transfer during post replacement — for panel fencing, support the panel temporarily with a prop or temporary post; do not leave panels hanging unsupported for more than a few hours
• Gravel board replacement — inspect gravel boards when replacing posts; if timber gravel boards have rotted, replace with concrete gravel boards at the same time — it is the best opportunity to upgrade
• Cost comparison — spur repair: 0.5–1 hour per post; full post replacement: 1–2 hours per post including concrete break-out; full section rebuild: 3–5 hours per 3 m bay

Quick Reference Table

Detailed Guidance

Diagnosing What Has Failed

Before pricing any fence repair, walk the fence line and identify all failures. A systematic check prevents arriving on site to repair one post and finding three more have the same problem.

Post failure check:

• Push firmly at head height; wobble indicates either rot or shallow/insufficient concrete
• Check the post at ground level: scrape back soil and probe with a bradawl; soft pulpy timber confirms rot
• Look for the fence leaning in one direction — the post(s) at the lean point have failed

Panel/board failure check:

• Walk along both sides; look for boards with rot at base (brown, softening), boards that have split along the grain, or panels where the frame has opened at corner joints
• Inspect arris rails: rails that have dropped at one end have either lost their bracket/mortice fixing, or the post they fix to has moved

Gravel board condition:

• Probe timber gravel boards with a bradawl at the post ends — this is where gravel board rot starts
• Concrete gravel boards: check for cracking or spalling; minor surface cracks are cosmetic, cracks through the full section require replacement

Spur Post Repair: Step by Step

1. Excavate alongside the failed post: remove soil on one side (typically the side not occupied by the fence boards) down to 600–700 mm depth. Keep the excavation tight — no wider than necessary to fit the spur.

2. Break the concrete away from the existing post base using a cold chisel and club hammer. You do not need to remove the entire concrete block — just clear enough concrete from one side of the post to allow the spur to seat against the timber cleanly.

3. Cut the rotted post base flush with the concrete block top or just above ground level, using a handsaw or reciprocating saw. This removes the worst of the rot and provides a clean face for the spur to sit against.

4. Position the concrete or steel spur in the excavated hole against the post face. The spur bolt holes or U-channel should align with the above-ground section of the post.

5. Brace the spur plumb in the hole. Use temporary timber wedges or a spare post off-cut to hold the spur against the existing post while you pour concrete.

6. Pour C20 concrete (or Postcrete) into the hole around the spur base. Fill to within 75 mm of the surface, crown and slope away from the spur. Allow 48 hours cure.

7. Drill through timber and spur for the coach bolt fixings. Drill slightly undersize (9 mm for M10 bolts) for a tight fit. Fit coach bolts with washers on both faces; tighten to snug — overtightening on rotten timber compresses the wood and weakens the joint.

8. Check the fence line is back to plumb and the spur is not introducing lateral lean.

Full Post Replacement

Where a spur repair is not suitable (post so rotten it cannot be bolted to; aesthetic requirement for matching appearance; full post stock needed for panel fence), full post replacement is required.

With concrete-set post:

1. Probe for rebar or anti-pull devices in the original concrete — pull wire fencing sometimes has concrete anchored to the post base; leave this in place and work around it.

2. Break out the concrete: cold chisel and club hammer; a SDS rotary hammer with a chisel bit makes faster work of a large concrete block. Work around the block perimeter and lever each piece out.

3. Remove the post and all concrete fragments from the hole; clean the hole sides.

4. Set the new post to correct depth (600–750 mm) in the enlarged hole; temporary bracing in two directions.

5. Pour concrete; cure 48 hours; fix fence.

Without concrete breakout (where a larger hole is acceptable):

Dig a new hole adjacent to the old post position, set the new post, transfer the fence to the new post, then leave the old rotten post and concrete block in the old hole — fill the old hole with concrete or compact soil. This adds about 10 cm to the visual post width but saves significant break-out time. Acceptable in garden positions where visual impact is secondary.

Arris Rail Repair

Arris rails fail at their fixings (bracket or mortice joint) more often than they rot through, because they are largely protected from ground moisture. Repairs:

Dropped arris rail: If the rail has dropped at one end (no longer horizontal), the fixing has failed. Refix using a pressed galvanised arris rail bracket (100 × 75 mm to match the rail section), screwing through the post face on 75 mm no. 10 screws. Do not try to re-mortice a dropped rail into timber without specialist joinery tools — use the bracket.

Snapped or rotten arris rail: Cut the failed rail back to clean timber at each end. Splice in a new arris rail section of the same section using twin fixing brackets at the splice joints. The splice can occur at any point in the span — it does not need to be at a post.

Frequently Asked Questions

How can I tell if the fence post repair spur will hold as well as a new post?

A correctly concreted repair spur (600 mm in ground, 300 mm hole diameter, C20 concrete) will resist essentially the same overturning moment as a correctly set new post of equivalent depth. The critical variables are the depth of the spur in the ground and the quality of the bolt connection to the above-ground timber. If the above-ground timber is at all soft or spongy, the bolt fixings will not hold reliably and a full new post is the correct repair.

The fence post is set against a wall — can I use a wall bracket instead of re-concreting?

A post bracket bolted to a masonry wall is a perfectly acceptable repair for a post adjacent to or against a wall. Use M10 or M12 expansion bolts into the masonry (Hilti HIT-RE 500 or equivalent; follow manufacturer's edge and spacing distances). The bracket should transfer the fence load into the wall at multiple bolt points. This is often simpler than digging against a wall foundation.

My client wants to replace three panels but leave the fence posts — is the spacing correct for new panels?

Measure the post spacing (inside face to inside face) before ordering panels. If posts have moved from their original position — which commonly happens over time as concrete shifts — the spacing may no longer match standard 1830 mm panel width. Order panels to the measured spacing, or adjust one post position when all three are being replaced in sequence. Never assume standard dimensions.

Regulations & Standards

• BS 1722-5 — Specification for close-boarded fences; post dimensions and concrete specification; applicable to repairs maintaining the original specification

• BS 1722-11 — Specification for wooden fence panels; relevant to panel replacement

• Building Regulations Part P — not relevant to fence repairs; fence work is not notifiable electrical work

• Jacksons Fencing Repair Guide — practical guidance on post repair and replacement

• Forest Research — Wood Decay and Preservation — decay mechanisms in fence posts and treatment guidance

• RoSPA / Planning Portal — Fence Ownership and Repair — guidance on boundary ownership and maintenance obligations

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