← All guides · Guide · Richard Lim

Spotting post rot before the fence goes over

A timber fence post does not tell you it is failing until it has already failed. By the time the fence is leaning, the post has usually rotted through at ground level and is only being held up by the concrete around it. Here is how to spot the problem before the whole run goes over.

The failure mechanism

Timber posts rot at ground level. The concrete footing traps moisture against the post at the soil interface. That interface is where wood-decay fungi thrive: warm in summer, wet in autumn and spring, and never dries out fully in winter. Once the fungal decay starts, the post loses structural cross-section from the inside out. The visible timber above ground can look fine right up to the day the fence leans.

The screwdriver test

The most reliable early check is a screwdriver push. Take a normal Philips or flathead screwdriver, walk down the fence line, and push the tip of the screwdriver into the timber post 100mm above ground level. Firm timber gives you no more than 2 or 3mm of penetration and the tip pulls out clean. Rotted timber lets the screwdriver in 10mm or more with light pressure, and the tip comes out wet or with soft fibres attached. That is your failing post.

The rock test

Two-hand grip on the post at chest height, gentle push and pull. A sound post gives you no movement at the top. A rotted post lets you move the top of the post 20 to 50mm each way, because there is no longer solid timber at ground level holding the base. Anything more than 10mm of movement on a 6ft fence post is a warning.

Ground-line inspection

Where the fence line allows it, dig a small hole down the side of the post to check the timber at ground level and just below. Look for: blackened timber (fungal decay), soft crumbly wood (advanced rot), a distinct waist where the cross-section has narrowed (structural loss), or beetle exit holes (secondary damage). Any of those and the post is on borrowed time.

The Broadstairs coastal-belt specifics

On the salt-air belt (Viking Bay, Stone Bay, Kingsgate, North Foreland) timber posts fail at 8 to 12 years typical, sometimes as fast as 6 years on the most exposed clifftop plots. Inland Broadstairs (St Peter's, Reading Street, Westwood) gets 12 to 20 years from the same spec of timber post. If your fence is at the tail end of that range and you have not checked the posts, it is time to check the posts.

What to do when you find rot

Options in order of cost: concrete-set the failing post with an added support brace (£50 to £100, buys you 1 to 3 years, cosmetic), replace the post like-for-like in timber (£80 to £150 per post, buys 8 to 15 years on the coastal belt), replace with a concrete slot post (£120 to £180 per post, buys 25+ years and stops the problem forever). On the coastal belt we default to the concrete-post answer because the timber replacement is a temporary fix in salt air.

Full-run considerations

If two or more posts on a 15m run are rotted, the whole run is at end-of-life and full replacement is usually cheaper than serial post replacement. WhatsApp us a photo of the run, the post spacings, and any obvious rot, and we come back with side-by-side numbers for repair vs replacement.