Rust on a metal fence: when a coat of paint is enough and when it needs welding

How to tell surface rust from rust that has gone into the metal

Surface rust sits on top of the steel as an orange-brown film or flaking scale. Scrape it with a screwdriver or a wire brush and you reach solid grey metal underneath, with the original thickness intact. This is by far the more common finding, and it is cosmetic rather than structural.

Rust that has gone into the metal looks different once you scrape it: the surface is pitted, uneven, or crumbles rather than flaking off cleanly. Tap the section with a hammer and listen. A dull, soft thud instead of a solid ring is a sign the wall of the tube or post has thinned. On box-section posts and rails, this often shows first at seams and low down near the ground, where moisture sits longest.

What to check before deciding anything

Before treating rust as either purely cosmetic or purely structural, look at where it sits. Rust on a flat panel or a mid-span rail rarely threatens the fence even if it looks bad. Rust at a post base, at a gate hinge, or at a welded joint is worth taking seriously, because these are the points carrying load.

Check for movement as well as appearance. Push a post sideways by hand: any give at ground level, beyond a slight flex you'd expect from a tall fence, suggests the base has weakened. Open and close a gate and feel for sag or drag, which often means a hinge weld has begun to fail rather than simply loosened.

• Scrape rust back to bare metal and check if it flakes off or crumbles
• Tap suspect sections with a hammer and compare the sound to solid metal nearby
• Push posts and gate leaves by hand to feel for movement at the base or hinges
• Look closely at welds and seams, where rust usually starts first
• Note whether the fence was galvanised or only painted, since that changes how deep rust typically runs

If the rust is only on the surface: cleaning and paint

For surface rust, the job is straightforward and well within reach for most owners. Wire-brush or grind the rust back to clean metal, feather the edges of any remaining sound paint so the new coat doesn't sit on a hard ridge, and wipe the surface free of dust before applying anything.

Use a metal primer suited to exterior steel, ideally one with rust-converting or rust-inhibiting properties, then finish with an exterior metal paint or a suitable enamel. Two thin coats outlast one thick one, and painting in dry weather above around 10°C gives the coating time to cure properly before rain or frost reaches it.

This is a job we're happy to see owners do themselves. If the fence is long, awkwardly shaped, or you'd rather not spend a weekend on it, our fence repair and installation work, from 45 € per hour, covers cleaning, priming, and repainting as a straightforward hourly job.

If the rust has reached into the metal: welding or replacement

Once rust has thinned the metal rather than just sitting on top of it, paint alone will not restore strength, it will only slow the next stage. A post with a rusted-through base, a rail with a crumbling weld, or a gate hinge that has lost its grip needs either welding in a new section or full replacement of that part.

Welding repairs typically involve cutting out the affected length, welding in new steel of matching profile, and re-treating the joint against corrosion before repainting. Whether this is worthwhile depends on the rest of the fence: repairing one weak post on an otherwise sound fence makes sense, while a fence rusting through in several places at once often costs less to replace than to keep patching.

Our welding work starts from 55 € per hour for repairs like these, and where a fence or gate needs new posts, frames, or brackets fabricated rather than just patched, that falls under steel structures, quoted from 250 € per job depending on scope.

What is dangerous and what can wait

A gate that has begun to sag on its hinges is worth acting on promptly, since a hinge weld that fails suddenly can drop a heavy gate leaf without warning. The same goes for any post along a driveway or a slope where a fence leaning outward could come down onto a path, a car, or a neighbouring garden.

Surface rust on a fence that is otherwise solid and doesn't move underfoot or under a push is not urgent. It's worth treating before the next winter to stop it spreading, but it will not fail suddenly, and there's no harm in leaving it a season if other jobs come first.