Why preparation decides the outcome

Every repaint of historic ironwork is really a test of preparation. New paint will not hold where flaking scale, loose rust or a chalky old coating still sits underneath it. On Scottish ironwork this matters more than most, because our weather is unforgiving: driven rain, salt-laden air along the coast, and dozens of freeze–thaw cycles each winter. Water finds its way into any gap you leave behind, rust expands, and the coating lifts from below.

The good news is that good preparation is patient rather than aggressive. You are not trying to return a hundred-and-fifty-year-old railing to a factory finish. You are trying to give a sound, clean, slightly keyed surface that a primer will grip, while keeping every casting mark, moulding and rivet that makes the piece worth caring for.

Know what you are working on

Before you pick up a tool, identify the metal and the coatings. Most Victorian and Edwardian street furniture is cast iron, poured in Scottish foundries and often stamped with a name, a number or a small pattern mark. Cast iron is brittle and slightly porous, with a graphite-rich skin that can make paint behave oddly if it is not keyed. Wrought iron, by contrast, is fibrous and forgiving, and is more common in older railings and structural straps.

Old coatings are usually a stack: tar, bitumen, red lead, oil-based gloss, sometimes a later water-based layer. Test small areas with a scraper and a solvent. Useful checks include:

• Whether coatings lift in flakes or soften into a sticky mess.
• Whether rust is surface bloom or deep, laminated scale.
• Whether the metal is pitted, cracked at joints, or has been welded or repaired in the past.
• Whether there is a foundry stamp, casting seam or historic repair worth preserving.

Removing rust and failed coatings without losing detail

Work from the gentlest method that will do the job. Start with hand tools: stiff nylon brushes, a shave hook, a window scraper with a rounded edge, and brass wire brushes rather than steel. Brass is softer than the iron and will not embed fragments that later bleed rust through the paint. On fine decorative work, a bamboo skewer or a wooden scraper gets into the corners of foliage and scrolls without rounding them off.

For tougher scale, a needle gun or a small electric chipping hammer is excellent, but keep the tool moving and never sit on one spot. Abrasive blasting can be appropriate on plain surfaces, using a fine, low-pressure medium such as garnet or olivine at around 30–50 psi. Coarse grit at high pressure will erase crispness in minutes and cannot be undone.

Avoid angle grinders with flap discs on decorative castings. They flatten mouldings and polish away the very texture that tells you the piece was hand-cast. Chemical strippers are useful where paint is thick and detail is fine, but check they are suitable for the coating and neutralise thoroughly afterwards. Rust converters based on phosphoric acid can stabilise light bloom, though they are not a substitute for removing loose material.

Deal with foundry marks, pits and hidden moisture

Once the bulk is off, inspect what remains. Small pits will always hold a little rust, and that is acceptable if the surrounding metal is sound. Clean them out with a wire brush and let the primer fill them. Deep, weeping rust at joints, cracks in castings and open seams need attention first — sometimes a conservator or blacksmith should look at them before paint goes anywhere near.

Cast iron hides moisture in its pores, particularly after a wet Scottish autumn. Blow out crevices with dry compressed air, then leave the piece in dry, ventilated conditions for as long as you can. A day or two is better than an afternoon. If you are working on site, choose a dry spell and check joints with a moisture meter where possible; painting over damp iron simply traps the problem.

Priming while the surface is still fresh

Bare iron begins to flash-rust within hours in damp air, so prime the same day you finish preparing — ideally within a few hours. A zinc phosphate or zinc-rich primer suits historic ironwork well, followed by a high-build undercoat and a durable topcoat. On structural pieces, micaceous iron oxide builds a tough, water-resistant layer that weathers gracefully.

Apply the first coat thinly and work it into pits and corners with a brush rather than a roller. Pay particular attention to the tops of railings, where water sits, and the bases, where splash and dog fouling attack the coating. Spot-prime any areas you had to clean back during the day before you stop work.

Weather, timing and the next forty years

Check the forecast and the thermometer. Most paints need at least 5°C and a surface temperature comfortably above the dew point, usually by around 3°C, so avoid early mornings and late afternoons when condensation forms. Shade from direct sun if the surface is too hot to touch, and never paint in wind-blown rain or when rain is expected within the drying window.

Finally, keep a record. Note the coatings used, the date, the weather and any areas left as found. Well-prepared ironwork with a sensible paint system will hold for fifteen to twenty-five years, and the next person to care for it will thank you for the notes — and for leaving the details intact.