Concrete posts vs timber posts on the Sandwich marsh

The choice most homeowners here should default to

If you are building or rebuilding a fence anywhere on the marsh side of Sandwich, or on a plot boundary facing Sandwich Bay, concrete posts with a 300mm gravel board are the correct answer and timber posts are the false economy. Inside the sheltered parts of the walled town or in a mid-plot fully sheltered garden, timber posts are still a fair call. That is the whole decision in two sentences. The rest of this page is why.

Timber posts - the honest cost curve

A treated softwood 100x100mm post concreted in properly costs less to buy, is quicker to install, and looks the same as a concrete post from six feet away. On sheltered ground away from the water table, it will run 15-20 years. That is a real service life.

On Sandwich marsh clay, that number drops to 8-12 years. The reason is the water-table cycle at the post base. Even a pressure-treated post is only preservative-loaded to a certain depth from the surface, and the cycling wet then dry then wet is exactly the environment the treatment is not designed for. The failure is not visible until the post moves, and by then it is already gone.

Concrete posts - the honest cost curve

Slotted concrete posts cost roughly £25-£40 per post more than timber. Installation is the same time. The panels or gravel boards slot into the concrete post grooves - no nailing to the post face required, which is quicker.

Service life of the concrete post is "indefinite" on any reasonable timescale. What you are actually paying for is a post that outlives three or four cycles of the fence face on top of it. When the panels or closeboard face wears out in 15-25 years, it is a straight-face swap onto the same posts, no post work, no ground work.

The ten-year total-cost comparison

For a 20-metre run in Sandwich marsh conditions, replacing panels only:

• Timber-post build - year 0: £1,400 install. Year 8: £1,100 to replace posts and rehang panels. Year 15: face swap, £600. Ten-year cost of ownership: around £2,500.
• Concrete-post build - year 0: £1,700 install. Year 8: no post work needed. Year 15: face swap only, £600. Ten-year cost of ownership: £1,700 (plus £600 in year 15, but that would happen either way).

Concrete is cheaper over ten years despite being more up front, and considerably less hassle. That is why we default to it.

The exceptions

1. Conservation-area frontage. Sometimes Dover District Council will accept timber posts and refuse a concrete-post look on a listed frontage. In that case we'll build in timber with the honest expectation of shorter life, and price the future replacement into the conversation up front.
2. Fully sheltered rear garden well away from marsh ground. If you are inside the town, three buildings deep, on drier ground, timber is fine and you will get closer to the 20-year top of the range.
3. Temporary or budget-constrained work. If the fence only needs to hold five years - selling the property, moving out, boundary before a rebuild - timber is the correct call for cash reasons.

What the upgrade looks like as a retrofit

If you already have timber posts and want to convert without a full rebuild, this is a common job for us. Panels come off, timber posts come out, holes widened slightly for the concrete-post base, concrete posts concreted in with the same panel run rehung. £45-£70 per linear metre depending on how much of the existing face is worth keeping. Two days on site for a standard 20m run. Fence looks the same from the neighbour's side and lasts three times as long.

What we won't do

Put concrete posts on a sloped run without gravel boards. The gravel board is not optional - it handles ground movement and keeps the panel face off ground water. If a customer wants concrete posts without gravel boards to save cost, that is a "no" from us. We'll walk away rather than build a fence that will fail in five years with our name on it.