Stainless steel
well suitedExcellent until the wrong grade meets salt, and then it stains like anything else.
- Surface heat: The surface here peaks near 148°F.
- Heat cycling: Repeated expansion and contraction is what opens joints and lifts finishes.
- Mildew and algae: Anything that stays damp grows something, whatever it is made of.
- Staining: Tannin from leaves, sunscreen and red wine are the three that actually mark outdoor surfaces.
A wash once a year
Ask the supplier: Is it 304 or 316? Within a few miles of salt water that difference is the whole decision.
Tea staining on coastal stainless is cosmetic corrosion and is very common in grade 304.
Weathering steel
well suitedIt is meant to rust, and the whole question is whether the rust ever stabilises where you are putting it.
- Surface heat: The surface here peaks near 148°F.
- Heat cycling: Repeated expansion and contraction is what opens joints and lifts finishes.
- Mildew and algae: Anything that stays damp grows something, whatever it is made of.
- Slow drying: This family gives water back quickly, which is most of the battle here.
Nothing to do
Ask the supplier: Is this a genuine weathering grade, and what does the datasheet say about wet-dry cycling and about run-off staining?
Weathering steel depends on repeated drying and sufficiently low chloride exposure to develop a protective patina. Persistent wetness, coastal salt, detailing and runoff can defeat that behavior; structural suitability remains an engineering/specification question.
Powder-coated aluminium
well suitedLight, rust-proof, and entirely dependent on the quality of its coating.
- Surface heat: The surface here peaks near 148°F.
- Heat cycling: Repeated expansion and contraction is what opens joints and lifts finishes.
- Mildew and algae: Anything that stays damp grows something, whatever it is made of.
- Slow drying: This family gives water back quickly, which is most of the battle here.
A wash once a year
Ask the supplier: Is the powder coat rated to AAMA 2604 or 2605, and is the substrate marine-grade?
Aluminium does not rust, but a scratched coating in salt air still corrodes underneath and lifts.
Hot-dip galvanised steel
well suitedSacrificial zinc doing a quiet job for twenty years, then not.
- Surface heat: The surface here peaks near 148°F.
- Heat cycling: Repeated expansion and contraction is what opens joints and lifts finishes.
- Mildew and algae: Anything that stays damp grows something, whatever it is made of.
- Slow drying: This family gives water back quickly, which is most of the battle here.
A wash once a year
Ask the supplier: Is it hot-dip galvanised or electroplated? The difference in service life is measured in decades.
Any cut or drilled edge is unprotected steel unless it was treated afterwards.
Powder-coated mild steel
workableHandsome and heavy, and it starts rusting from the first chip.
- Surface heat: The surface here peaks near 148°F.
- Heat cycling: Repeated expansion and contraction is what opens joints and lifts finishes.
- Mildew and algae: Anything that stays damp grows something, whatever it is made of.
- Slow drying: This family gives water back quickly, which is most of the battle here.
Oiling or repainting each year
Ask the supplier: What is under the powder coat, and is there a primer or a galvanised layer beneath it?
Rust starts where the coating is broken, which is almost always at the feet.
Wrought and cast iron
workableBeautiful, permanent-feeling, and a repainting commitment forever.
- Surface heat: The surface here peaks near 148°F.
- Mildew and algae: Anything that stays damp grows something, whatever it is made of.
- Heat cycling: Repeated expansion and contraction is what opens joints and lifts finishes.
- Slow drying: This family gives water back quickly, which is most of the battle here.
Oiling or repainting each year
Ask the supplier: How was it finished, and what is the recommended repainting interval here?
Cast iron in freeze-thaw conditions can crack where water sits in a hollow section.