Can cast aluminium doors rust? Corrosion, fading and a care routine

Short answer: A cast aluminium door does not rust like an iron door: its oxide film, about 4 nm thick, grows back when scratched. But salty or sulphurous air, standing water, contact with other metals and breaks in the coating can still corrode it. Look after the finish, seals and hardware: clean to suit the site, touch up damage early, and take bigger problems to the factory.

Why does a cast aluminium door not rust like an iron door?

Because its oxide film protects it. As soon as aluminium meets air, it forms a dense oxide film about 4 nm thick. The film stops the metal underneath from oxidising any further, and when it is scratched, it grows back on its own.

The Aluminum Association puts it plainly: in the presence of moisture, aluminium will not rust as steel does. But the Aluminium Federation (ALFED) notes that the film is stable between about pH 4.0 and 8.5 and dissolves below 4 or above 8.5.

When can an aluminium door still corrode?

It can, in four common cases: salty or sulphurous air, standing water, contact with other metals, and breaks in the coating. These lead, in turn, to pitting, crevice corrosion, galvanic corrosion and filiform corrosion, a form that creeps under the paint.

• Pitting: ALFED says airborne salt (particularly chlorides) can cause pitting, and highly sulphurous air minor pitting, though pits are generally only a fraction of the material's thickness deep.
• Crevice corrosion: AMPP, the corrosion association, says it occurs under gaskets, fastener heads, deposits and lifted coating, where liquid stagnates.
• Galvanic corrosion: when two different metals touch and are wet, the less noble one corrodes first; ALFED says that is aluminium in most combinations.
• Filiform corrosion: AMPP says it develops under a breached protective film and normally starts at small, sometimes microscopic, coating defects.

What makes a door finish age and fade?

Mostly sun, dirt and damage. Dulux Powder Coatings lists ultraviolet light, salt and grime building up over time, wind-blown sand, and acidic or alkaline local conditions as factors in coating life. Standing water, scratches and the wrong cleaners also harm a finish.

Sun: UV makes coatings fade, chalk and lose gloss. Dulux says bright pigments such as reds, oranges, greens and blues suffer more from UV, and dark colours absorb far more heat. PPG explains that the demanding US coating standard FGIA/AAMA 2605 requires, after ten years in South Florida, colour change within 5 ΔE, chalk rating 8 or better and at least 50% gloss retained: half the gloss after ten years passes. That is a coating requirement, not a door result.

Salt, pollution and acid rain: TECHNAL, an aluminium window and door brand, notes salt build-up on the coast and rain-borne grime in cities. China's Ministry of Ecology and Environment reports that acid rain areas (annual mean rain pH below 5.6) covered about 2.0% of China's land in 2025, mainly south of the Yangtze and east of the Yunnan–Guizhou Plateau, including most of Zhejiang.

How do you clean a cast aluminium door?

Use warm water with a neutral detergent and a soft cloth, sponge or soft brush, then rinse with clean water and dry. Never use steel wool, sandpaper, scouring powder, strong acids or alkalis, or solvents such as thinners, turpentine, paraffin or citrus-based cleaners.

1. Rinse off loose dust and sand with a wet sponge or water first; do not wipe dry.
2. Add a little neutral detergent, such as washing-up liquid, to warm water; the aluminium systems company Reynaers specifies pH 6–8 and no ammonia. Use a soft brush in carved recesses.
3. For stubborn marks, Dulux recommends only isopropyl alcohol or methylated spirits, then a rinse.
4. Rinse off all detergent and dry with a soft cloth, leaving no water in recesses or the threshold.
5. Clean only when the surface is below 25 °C: in summer, early, late or on a cloudy day.

Dulux warns that damage from unapproved solvents can take up to twelve months to show; TECHNAL warns against polishes and cleaners for copper, silver or bare aluminium. During building work, cover the door with film or tape and remove it afterwards. ALFED notes that alkaline cement and mortar speed up aluminium corrosion, so remove cement or paint splashes before they dry.

How often should you clean it in different environments?

It depends on the site. Combining Dulux, Reynaers and TECHNAL advice: inland doors that get rain, at least yearly and ideally every six months; city and industrial sites, about every three months; the coast, every one to three months; doors rain never reaches, more often.

How do you check the seals, hinges and drainage?

Work through the checklist below every six to twelve months, looking above all for ageing seals, sagging hinges and blocked drainage holes. Reynaers recommends a check every six months for doors in normal use; TECHNAL recommends checking the seals once a year.

• Finish: after cleaning, scratches to bare metal, blisters, peeling or thread-like bumps under the paint.
• Colour: compare sunny and shaded faces; rub with a finger for powder.
• Seals: cracks, hardening, flattening, seals out of their groove, light through gaps when shut.
• Hinges and locks: a sagging or scraping leaf, noises, loose screws.
• Drainage: sand or leaves in drainage holes and the threshold channel, water standing after rain.
• Contact points: white or grey powder where added metal items, such as doorbells or camera brackets, touch the door.

Whether hinges need oil depends on the hardware instructions: TECHNAL advises a little lubricant on hinges and locks yearly, but Reynaers says its door hinges must not be lubricated and lock cylinders take graphite powder. Designs differ; if unsure, ask the factory.

Reynaers also recommends dusting EPDM seals with talc or wiping on liquid silicone yearly to prevent cracking, cleaning drainage chambers every six months and clearing blocked drainage holes. Drainage hole positions follow the order drawings.

What should you do if the finish fades or gets scratched?

For fading, clean first, then judge: if the colour comes back, it was dirt and salt; if it stays pale and a finger comes away powdery, it is sun ageing. For scratches, check whether bare metal shows; if it does, seal it with touch-up paint soon.

Even, slight fading and gloss loss are normal ageing: keep cleaning, and do not polish with paste or abrasives. Uneven fading, patchy heavy chalking, blistering or peeling call for the factory.

Clean and dry chips or scratches to bare metal, then dab on matching touch-up paint so water and salt cannot creep under the paint:

• Get touch-up paint in the order colour from the door's manufacturer; systems companies such as Reynaers also sell touch-up sticks: dab on, let dry.
• Do not sand large areas; TECHNAL warns that abrasives and polishes scratch aluminium and remove coatings.
• Touch-ups on site cannot repeat the factory's pre-treatment and high-temperature curing, so they suit small areas only, and colour and gloss may differ slightly.

When should you contact the factory?

When cleaning and touch-ups do not solve a problem, let the factory assess it. Before getting in touch, gather photos or video of the whole door and the problem area, the order specification sheet, and roughly when the problem started. Common cases:

• widespread fading or chalking, or clear colour differences between sunny and shaded faces;
• blistering, peeling, thread-like bumps, or peeling that returns after a touch-up;
• a sagging or scraping leaf, or loose or sticking hinges or locks;
• seals that need replacing in full lengths;
• plans to drill the door for metal fittings, or doubt about a cleaner.

The Reynaers manual reserves replacing fittings and taking leaves off for an authorised specialist; do not do it yourself.

Sources: Aluminium Federation (ALFED): aluminium corrosion, Fact Sheet 04/2020；The Aluminum Association: Guidelines for Minimizing Water Staining of Aluminum；AMPP (Association for Materials Protection and Performance): Forms of Corrosion；Dulux Powder Coatings: Care and Maintenance of Powder Coated Surfaces, New Zealand edition, 2021 (PDF)；Dulux Powder Coatings (Australia): FAQs on care and colour；Reynaers Aluminium: Professional care and maintenance brochure (PDF)；TECHNAL: How to look after aluminium windows and doors；PPG: FGIA/AAMA 2605 coating requirements；Ministry of Ecology and Environment of China: 2025 Report on the State of the Ecology and Environment, acid rain section (in Chinese)