# Zinc vs Aluminium Cladding: Patina, Coating Life and Detailing

> Zinc cladding develops a protective patina as it weathers, so its appearance changes and self-heals minor scratches, and it is worked in standing seam, interlocking panel or cassette form. Aluminium cladding relies on an applied finish — anodising or a coating system — for both appearance and protection, and holds its original colour as long as that finish lasts.

## 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

| Factor | Zinc | Aluminium |
| --- | --- | --- |
| Protection mechanism | Self-forming patina | Applied finish — anodising or coating |
| Appearance over time | Changes and develops | Holds original colour |
| Minor scratch behaviour | Weathers in over time | Remains visible; may expose substrate |
| Colour range | Natural greys and pre-weathered tones | Very wide |
| Weight | Heavier than aluminium | Light |
| Forming | Roll-formed, seamed, curved | Folded cassettes, crisp returns |
| Key corrosion risk | Copper contact, trapped moisture | Dissimilar metals, finish damage |
| Material cost | Higher | Wide range by system and finish |
| Ventilated back face | Essential | Recommended |

## 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.

## Frequently asked questions

### What is patina and is it a problem?

It is a stable surface layer that forms as zinc reacts with the atmosphere, and it is protective rather than a defect — it is what gives zinc its long service life without a coating. The practical consequence is that the facade's appearance changes over the first years and continues to develop, and it will not be uniform if different elevations see different exposure. That is accepted as the material's character, but the client needs to understand it before, not after.

### Which keeps its original appearance longer?

Aluminium with a high-quality finish, because the finish is designed to hold colour. A good fluoropolymer coating or a well-executed anodised finish maintains appearance for a very long time. The important qualification is that coating quality varies enormously — a commodity coating on the same panel can fade or chalk far sooner, and that difference is larger than the zinc-versus-aluminium difference.

### Does zinc need maintenance?

Very little in the ordinary sense, since there is no coating to maintain. What it does need is correct detailing, because the main risks are chemical and galvanic rather than cosmetic — contact with incompatible metals, run-off from copper, and trapped moisture against the back face. Those are design issues, addressed once at detailing stage.

### What are the corrosion risks with each?

For zinc, contact with copper or copper-bearing run-off, and prolonged moisture against an unventilated back face. For aluminium, contact with dissimilar metals in the presence of moisture, and damage to the anodised or coated layer exposing bare metal, particularly in coastal atmospheres. Both are handled by isolating dissimilar metals, ventilating the back of the panel and detailing so water drains rather than sits.

### Which is easier to form into complex shapes?

Both are workable, and each in a different way. Zinc is traditionally roll-formed and seamed, and lends itself to standing seam, interlocking panels and curved or faceted surfaces. Aluminium is readily folded into cassettes with crisp returns and concealed fixings, and is lighter to handle in large panels. The choice usually follows the intended visual language rather than a fabrication limit.

### How does cost compare?

Zinc is generally the more expensive material and is chosen for its appearance and longevity rather than on cost. Aluminium spans a very wide range depending on the panel type and the finish specified — a coated aluminium rainscreen and a premium anodised cassette system are different propositions. Comparing the two on material rate alone misses the fixing system, which is a substantial part of either installed cost.

## Sources

- [EN 988](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Zinc and zinc alloys — rolled flat products for building
- [EN 1396 / EN 1090](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Aluminium coil coating and execution of structures
- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings and structures
- [EN 13501-1](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Reaction to fire classification of construction products

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Source: https://hagerstone.com/compare/zinc-vs-aluminium-cladding