Why does my metal gate rust at the bottom, and how do I stop it?

Metal gates and railings almost never rust in the middle. They rust at the bottom of the uprights, at the bottom rail, and in the bottom of the hinge sockets, because those are the places water collects and stays. On a hollow section it usually starts inside, where nothing was ever painted, and by the time it shows on the outside a good deal of the wall thickness has gone.

Safety

What you'll need

• Wire brush, wire wheel or an angle grinder with a wire cup
• Rust-converting or rust-inhibiting primer
• Metal topcoat suited to exterior exposure
• Eye protection, gloves and a mask
• Drill for drain holes
• Replacement section and a welder, or a fabricator (optional)
• Cold galvanising paint (optional)

Step by step

1. Tap along the bottom of everything with a hammer.Sound metal rings; thin, corroded metal gives a dull thud and may perforate. Do this along the bottom rail, up each upright for 200mm, and around the base of any post. This tells you what is repairable and what is not, which is the whole decision.
2. Look for where the water is getting in and staying.Open tops of hollow posts, unsealed joints, the inside of the bottom rail, and the socket a gate post sits in. Then look at the ground — a gate whose bottom rail sits in a puddle or against soil is being asked to do the impossible.
3. Clean sound metal back properly.Wire wheel or a wire cup on a grinder, back to bright metal or at least to firm, tightly adherent surface. Feather the edges of any remaining sound paint. Paint applied over loose rust lifts within a season — the preparation is the job.
4. Deal with rust you cannot fully remove.In pitting and inside sections you cannot reach, a rust converter that chemically stabilises the surface is the practical answer. It is not a substitute for cleaning where you can clean, but it is far better than painting over active rust in a pit.
5. Prime with something intended for the job.A rust-inhibiting metal primer, or a zinc-rich cold galvanising paint on galvanised items where the coating has been breached. Zinc-rich coatings give sacrificial protection, which is a different and better mechanism than a barrier paint on a base metal.
6. Drill drain holes in every hollow section.A hole at the lowest point of each hollow member, and a cap or a plug on any open top. This is the change that actually stops it happening again — a section that drains does not hold a reservoir of water against its inside wall.
7. Get the gate out of the water.Raise the bottom rail's clearance if it is dragging in a puddle, improve the fall on the ground beneath it, or put a gravel strip under the gate line. A gate hanging over free-draining ground lasts a great deal longer than one over a puddle.
8. Cut out and replace what is too thin.Perforated or paper-thin sections are not repairable with filler or with paint. A fabricator can cut out a bottom rail or the base of an upright and weld in new section, and on an ornamental gate that is often much cheaper than replacement.
9. Topcoat properly and maintain it.Two coats of a metal finish suited to exterior exposure, brushed well into corners and into every joint. Then check it annually, particularly along the bottom, and touch up chips before they open up.

Tips

• Hot-dip galvanising a gate that is otherwise sound is genuinely worth pricing. A fabricator can arrange it, and a galvanised gate then only needs a decorative coat rather than a protective one.
• Never let soil, mulch or a border build up against a metal post. It holds moisture against the metal permanently and it is the commonest reason a post fails at ground level.
• Paint the inside of any section you can reach before you close it up. It is the one chance you will get.
• On an ornamental gate, photograph the detail before stripping. Matching a moulding or a scroll later is much easier with a reference.
• Wear a mask and wet the surface if the existing paint is old. Paint on older metalwork can contain lead and the dust is the hazard.

Common mistakes

• Filling rust holes with body filler — Filler does not restore strength and it seals damp corroding metal in behind it. On a structural member like a bottom rail or a post it is a repair that hides a developing failure.
• Painting over loose rust — The paint has nothing sound to grip and the corrosion continues underneath. It looks fixed for a season and comes back worse because the moisture is now trapped.
• Leaving hollow sections closed with no drainage — Every hollow section that can take water in will, through a joint, a hole or condensation. Without a drain hole it holds it against the inside wall permanently.
• Ignoring damaged galvanising — Galvanising protects sacrificially over a small breach, but a large exposed area of steel corrodes normally. Cut ends and drilled holes want cold galvanising paint the day they are made.

If it doesn't work

Keeping on top of it

• Check and clear drain holes in hollow sections (Yearly)
• Inspect the bottom 200mm of every member and touch up chips (Yearly, in autumn)
• Oil hinges and latch mechanism (Twice a year)
• Keep vegetation and soil clear of the gate line (Through the growing season)

Questions people ask