Timber posts almost always fail in the same 100mm band at ground level, where the wood is alternately wet and exposed to air. Understanding that one fact tells you which repair is worth paying for.
Diagnostic timeline
Work through these steps in order before booking a repair.
- 1
Push a screwdriver into the post at soil level — resistance means sound timber, easy penetration means rot.
- 2
Scrape away 50mm of soil around the base and look for black staining or fungal growth.
- 3
Check whether the rot is one post or repeats every second or third post along the run.
- 4
Tap the post: a dull, hollow sound at the base indicates internal decay.
Likely causes
Ground contact without gravel boards
Soil holds moisture directly against the post continuously.
Water sitting in the post hole
Concrete poured as a bathtub with no drainage beneath keeps the post standing in water.
Untreated cut ends
Posts cut to length on site without re-treating the cut expose untreated heartwood.
Age
Even good treated timber in contact with soil has a finite life; on many runs we attend the posts are simply time-expired.
Fix options, full-width
Concrete spur repair
Upper post is solid, rot is at the base onlyThe spur is set in concrete alongside and coach-bolted through the healthy timber. Panels stay in place; usually a same-day job per post.
Full post replacement
Rot extends up the post or the post carries a gateNew post set in concrete with a drainage layer, plus a gravel board so the new timber never contacts soil.
Convert to concrete posts
Several posts have gone on the same runSlotted concrete posts and gravel boards end the problem permanently; existing panels can often be reused.
Get this fixed properly
Free site visit across London and Hertfordshire, a written specification and a fixed price before anything starts.
Prevention
- Fit concrete gravel boards so the sacrificial element is not the post
- Add a hardcore drainage layer under each post before concreting
- Re-treat every cut end before the post goes in
- Keep borders and raised beds off the fence line
Frequently asked
Are concrete spurs a permanent fix?
They are a long-term fix when the remaining post timber is genuinely sound and the spur is based properly.
Can I replace one post without taking the fence down?
Usually. Adjacent panels are supported and lifted clear rather than dismantled.
Why do posts rot but panels look fine?
Panels are clear of the ground; the post is the only part permanently in the wet zone.
Will new posts match the old ones?
New treated timber is greener initially and weathers to match within a season.