Zinc vs Aluminium Cladding: Patina, Coating Life and Detailing

Two different propositions

This is not a like-for-like substitution decision. Zinc is chosen for how it weathers; aluminium is chosen for how it holds a finish.

A client who wants a facade that looks the same in year fifteen as on handover wants well-finished aluminium. A client who wants a material that ages and develops character wants zinc. Selling either as the other produces disappointment.

Side by side

The detail that protects zinc

Zinc's durability depends on it being able to dry. A panel with moisture trapped against the back face, unable to ventilate, corrodes from behind — which is invisible until it is advanced.

So a zinc facade needs a properly ventilated and drained cavity, a suitable separation layer where required, and careful attention to where water goes. It also needs to be kept clear of copper and of run-off from copper elements above, because that combination is aggressive to zinc.

None of this is difficult. All of it has to be decided at detailing stage, and it is the main technical reason to involve the facade specialist early rather than at procurement.

For aluminium, the finish is the decision

Two aluminium panels can be physically identical and perform completely differently over twenty years, because the finish is doing the work.

A high-performance fluoropolymer coating system and a commodity polyester coating look the same on day one. After sustained UV exposure and repeated monsoons, one has held its colour and gloss and the other has faded or chalked. Anodising behaves differently again, with its own thickness grades.

So the specification that matters is not "aluminium cladding" but the finish system, its grade and its warranty — and whether the warranty terms match the actual exposure of the building.

Coating and execution standards such as EN 1396 and EN 1090 are the reference points, and EN 988 covers rolled zinc flat products for building.

Both are systems, not sheets

Whichever metal is chosen, most of the installed cost and nearly all of the performance risk sits in the support system: the aluminium carrier framing, brackets, fixings, movement allowance and the ventilated cavity.

Panel size, thickness and fixing centres derive from design wind pressure under IS 875 (Part 3) for the specific building. Corners and parapets take the highest loading. This is facade engineering output, not a catalogue selection.

Mistakes that cost real money

• Selling zinc without explaining patina. The appearance will change; the client must expect it.
• Comparing metals without comparing finishes. For aluminium the finish is the durability.
• Allowing copper run-off onto zinc. A detailing error with a slow, expensive consequence.
• Blocking the ventilated cavity. Both materials need the back face to dry.
• Mixing dissimilar metals at fixings without isolation. Galvanic corrosion starts where nobody can see it.
• Pricing panels and forgetting the carrier system. It is frequently the larger number.

Standards referenced

Rolled zinc flat products for building to EN 988; aluminium coil coating and execution with reference to EN 1396 and EN 1090; wind loading to IS 875 (Part 3); reaction-to-fire classification to EN 13501-1. Panel sizing, fixing centres, wind pressure and the suitability of any finish for the building's exposure must be confirmed by the project's facade engineer and the manufacturer.