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How to paint rusty metal

Updated: 23 October 2026

You have a tin of direct-to-rust enamel and a rusty steel gate, a railing or a bistro frame, and the label sounds as if the brush can go straight on. It cannot. How to paint rusty metal, with these Hammerite tins, starts with what is loose and what is greasy. This is method, not a ranking. The [metal paint comparison](/hub/paints-and-varnishes/metal-paint) holds the seven listings. Peter F. updated this page on 23 October 2026 from Hammerite’s UK smooth page and the saved review notes. We did not run a lab test. A qualifying purchase through our links can earn a commission at no extra cost to you.

You have a tin of direct-to-rust enamel and a rusty steel gate, a railing or a bistro frame, and the label sounds as if the brush can go straight on. It cannot.

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Hammerite Hammerite 5158235 smooth black

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Hammerite Hammerite 5158235 smooth black
9.4/10about £20.43
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Hammerite Hammerite smooth black 750 ml

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Hammerite Hammerite smooth black 750 ml
9.4/10about £22.00
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Hammerite Hammerite smooth black 250 ml

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Hammerite Hammerite smooth black 250 ml
9.2/10about £9.97
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On this page
  1. 1.What you still remove
  2. 2.How the coat goes on
  3. 3.Time, temperature and the brush
  4. 4.When this method is the wrong page

What you still remove

Direct to rust means you do not grind every bar back to bright metal. It does not mean you paint over flakes, scale and oil. Hammerite’s advice is a wire brush for loose rust and flaking paint, then a wash so grease is gone. Tight stain can stay. Anything that lifts has to go. Wash with detergent or sugar soap and let the metal dry. A patch test on the old film, left for about an hour, tells you whether that film is sound. If it wrinkles or lifts, it is not a base. One garage-door note used an undercoat anyway. That is a reviewer’s choice. If the old paint may contain lead, which HSE says lingered into the early 1980s, do not dry-sand it and do not use a blow lamp. Wet methods, and children kept out of the dust, are the HSE line. A large area in an occupied home is a professional job.

How the coat goes on

Do not thin the paint for a brush. Hammerite’s UK page says the enamel is ready to use. A spray-gun note of about 15 percent is a workshop method, not a reason to pour white spirit into a domestic tin. Solvent enamel indoors is a point where you stop and call someone. Load the brush lightly. One coat is for sound old paint that passed the patch test. Two coats go on bare or rusty metal. A thick coat sags, and going back over the wet film lifts it. Reviews of the 750 ml black tin call it treacle. Lay a section and leave it. A good brush left standing in the paint is the one reviewers say is ruined. Both faces and the bottom bar are on metal paint for gates and railings.
Hammerite Hammerite 5158235 smooth black

Testsieger

Hammerite Hammerite 5158235 smooth black
9.4/10about £20.43
View offer

Time, temperature and the brush

Hammerite’s UK page asks for about 8°C to 25°C. A trade sheet’s upper band of 30°C is a clash, not permission for a hot afternoon. Touch dry is about 1–2 hours. Recoat after 4 hours, not the listing that prints both 24 hours and 4 hours. Warm weather is when the tin skins. Keep the lid on between sections, and do not flood the brush. Working a section that has already flashed off lifts the film. Do not empty the tin, the brush wash or the rinse into a drain. The sheet warns of a flammable liquid, drowsiness and harm to aquatic life. Ventilate. The 250 ml black bullet prints a flash point of 32°C. That is the liquid, not a cure time.

When this method is the wrong page

This order is for rusty or bare ferrous steel. Bare galvanised steel, zinc and aluminium need Hammerite Special Metals Primer first. None of these ASINs is that primer. A new zinc-coated gate painted with Direct to Rust is the wrong job even if you wire-brush it. The buying guide, linked below, separates that fork. A hot radiator is the other exit. Outdoor enamel has no service temperature in these listings. Stop and call a professional for structural steel on a named ISO 12944 system, for large lead-paint removal in an occupied home, for spraying solvent enamel indoors, and for a salt-coast gate that needs more than a DIY one-pack film. A bistro set after a light sand is the job these reviews describe.

Common questions

Do I have to remove all the rust?
You remove what is loose: flakes, scale that lifts, and flaking old paint. Tight stain can stay, which is the point of a direct-to-rust enamel. You still wash grease off. Layered scale is not the same as a tight stain. Painting over a flap of rust is why the film fails at the edge a season later.
How many coats go on bare steel?
Two coats on bare or rusty ferrous metal. One coat only where the previous paint is sound and a patch test has held for about an hour. Recoat after about 4 hours. A single heavy coat sags, and brushing back into it while it is wet lifts the film. Edges need the same two coats.
Can I thin it so the brush moves?
Not for a brush or a roller. The UK page says the enamel is ready to use. If it feels like treacle, use a light load and a brush you are willing to discard, not white spirit in the tin. A spray figure of about 15 percent is for a gun, not a home recipe.
Why did the paint lift when I brushed back over it?
The enamel flashes off quickly in warm weather, and a second pass through a film that has started to set pulls it off the metal. Reviews of the 750 ml black tin say that. Lay a section and leave it. If you missed a patch, wait about 4 hours and put the next coat on. Flooding the brush makes the lift worse.
When should I stop and call someone?
Stop for a specified structural system, for a large area of possible lead paint in a lived-in house, for spraying solvent enamel indoors, or for a salt-coast gate when a one-pack film is all you have. Also stop on bare galvanised steel or a hot radiator. A garden gate you can wire-brush on a dry day in the temperature band is the job this page is for.

Related pages

Metal paint buying guide

Radiator paint versus metal paint

Metal paint

Best metal paint UK for your garden gate or panels

Metal paint for gates: edges, underside and tin size

Sources

Public sources from the research digest, last checked on 22 October 2026. Shelf prices and star lines are the stored amazon.co.uk figures. The price band is this set, not a market average. No listing was lab-tested.

  1. Hammerite Direct to Rust metal paint, smooth finish (retrieved 22 October 2026)
  2. Hammerite surface preparation (retrieved 22 October 2026)
  3. Hammerite: how to paint a radiator (retrieved 22 October 2026)
  4. VOC in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012 (retrieved 22 October 2026)
  5. HSE: lead in paint (retrieved 22 October 2026)
  6. HSE: GB CLP hazard labels (retrieved 22 October 2026)
  7. SteelConstruction.info: standard corrosion protection systems (retrieved 22 October 2026)
  8. Rust-Oleum UK radiator paint (retrieved 22 October 2026)