Why metal gates streak — and why it usually happens before you open the tin

Streaks on a painted gate nearly always come from one of four things: a coat applied too thickly, a brush dragged back over paint that has already begun to skin over, a surface hot enough in direct sun to dry the paint on contact, or rust and flaking old paint left sitting underneath. None of these are difficult to avoid, but they all have to be dealt with before you start. The good news is that a smooth, factory-looking finish is mostly about preparation and patience rather than expensive equipment. A decent 50mm brush, a small foam roller, a wire brush and a dry, mild afternoon will get you most of the way there.

This guide covers the practical route for the gates most British homes actually have — wrought-iron style driveway gates, galvanised steel side gates, and the older mild steel gates that have been repainted four or five times over the decades.

Preparation: clean, scrape and treat what you find

Paint will not hide a bad surface, it magnifies it. Start by washing the gate down with warm water and a little washing-up liquid to shift dirt, algae and traffic film, then rinse and let it dry fully. A degreaser is worth using near hinges and latches, where hand grease and oil build up and will cause paint to crawl and blister.

• Loose and flaking paint: scrape back to a firm edge with a shave hook or putty knife, then feather the edges with 80–120 grit abrasive paper so you cannot feel a step.
• Rust: wire-brush back to bare metal where you can. For light surface rust in pits and welds, a rust converter is a sensible shortcut — it neutralises the rust and gives a firm base to prime over.
• Galvanised steel: new galvanising is slick and paint struggles to grip. Either leave it to weather for six months or wipe it down with a proprietary etch primer or a diluted vinegar wash, then rinse thoroughly.
• Chalky, powdery old paint: if a white dust comes off on your hand, the coating is breaking down and needs removing, not painting over.

Once the gate is clean and dry, give it a final wipe with a cloth dampened with white spirit to remove dust and any residual oil.

Priming bare patches and rusty spots

You only need to prime where bare metal is showing — spot-priming is fine and saves both time and money. Use a zinc phosphate or red oxide primer for ferrous metal, applied in thin coats with a small brush, working it into pits and around welds rather than laying it on thickly. Two thin coats are always better than one heavy one.

If you are painting over a rust converter, check the tin for the recoat window and follow it precisely; most need a full 24 hours before priming, and some need longer in cool, damp weather. Never prime over damp metal. On a cold morning, condensation sits on steel invisibly, and trapped moisture under primer is exactly how a gate starts blistering within a season.

Choosing the right paint and tools

For exterior metal, you want a paint designed for the job — a solvent-borne exterior metal gloss or a direct-to-metal enamel. Solvent-borne paints flow out better and leave fewer brush marks, which is exactly what you want on a gate. Water-based exterior metal paints are quicker to dry and lower in odour, but they can flash-rust on bare steel, so use them only over a properly primed surface.

• Brush: a 50mm synthetic brush for water-based paint, a natural-bristle brush for solvent-borne. Keep a small 25mm brush for rails, finials and scrollwork.
• Roller: a 100mm foam roller for flat bars and panels. Foam leaves no texture, which is why it beats a fluffy roller here.
• Thinners: white spirit for solvent-borne paint, clean water for water-based. Thin only as much as the tin allows — usually no more than 10 per cent.

Stir the paint thoroughly rather than shaking it. Shaking traps air bubbles that pop on the surface and leave tiny craters. If a skin has formed in the tin, lift it out whole rather than stirring it through.

Technique: thin coats and the art of laying off

Two thin coats, not one thick one. Thick paint sags, dries unevenly and shows every brush mark. Load the brush lightly, tap off the excess, and work in sections of about a metre at a time so you always keep a wet edge to blend into.

The trick that separates a professional finish from a streaky one is laying off. Once a section is covered, run the brush lightly along the full length of the bar in one continuous stroke, in one direction only, with just the tips of the bristles touching the paint. Do not go back and forth. Two or three light passes and stop. On flat rails, roll the paint on first, then lay off with the brush to flatten the roller texture.

Avoid painting in full sun or on a hot gate. Move to the shaded side if you can, or work early in the morning. Paint that dries too quickly cannot level itself, and that is where most streaks come from.

Weather windows, drying times and annual checks

Metal paint needs the right conditions as much as the right technique. Aim for a temperature between 10°C and 25°C, with low humidity and no rain forecast for at least 24 hours. Avoid painting if the dew point is within 3°C of the air temperature, as condensation will form on the fresh paint overnight.

• Recoat: usually 16–24 hours for solvent-borne paint, 4–6 hours for water-based. Check the tin — cool weather stretches these times considerably.
• Cure: allow around seven days before wiping the gate down or closing latches hard against the paint.
• Aftercare: inspect each spring for chips and rust bleeds, particularly along the bottom rail where road spray and wet grass hit. A quick spot-prime and touch-up takes minutes and adds years.

A gate painted properly should hold its finish for five to eight years. Keep it clean, touch up chips promptly, and keep hinges and latches lightly oiled so the gate swings freely rather than flexing and cracking the paint around its joints.