# Aluminium Composite Panel (ACP) — Cladding and Signage Specification

> An aluminium composite panel (ACP) is two thin aluminium skins bonded to a core, finished with a factory coil coating. It is light, very flat and can be routed and folded into cassettes. Its facade performance turns on four choices: the core grade, the coating (PVDF for exteriors), the skin thickness, and the fixing and joint system. Signage-grade sheet is not facade-grade sheet.

## What it is, and what the choice turns on

An **aluminium composite panel** is a sandwich: two thin aluminium skins
bonded to a core, with a factory coil coating on the face. It is light, very
flat for its weight, and can be routed and folded into cassettes with crisp
returns, which is why it is the default for facade cladding, canopies,
fascias and signage.

The decision a client actually faces is not "ACP or not". It is which grade.
Panels that look identical on delivery differ in core, coating and skin
thickness, and those differences decide whether the facade still looks right
after several monsoons, whether it passes the fire review, and whether a
damaged panel can be replaced. The usual failure is substitution: a cheaper
signage-grade or different-core sheet arriving under the same product name.

## Anatomy of a panel

| Layer | What it does | What to specify |
| --- | --- | --- |
| Face coating | Colour, gloss and weathering life | Coating type (PVDF, FEVE or polyester) and the performance standard it meets |
| Face skin | Stiffness, dent resistance, flatness | Alloy and skin thickness, from the manufacturer's data |
| Core | Bonds the skins; decides fire behaviour | Core grade with the tested reaction-to-fire class for that product and thickness |
| Back skin | Balances the panel so it stays flat | Same alloy family, with a service coat |
| Bond | Holds skins to core over the panel's life | Peel strength test evidence |
| Protective film | Protects the face until installation | Removal within the period the manufacturer states |

Facade panels are typically a few millimetres thick overall with skins of
around half a millimetre each, while signage and interior sheets often use
thinner skins. The exact figures belong to the manufacturer's data and the
facade engineer's design. In India, the product standard for aluminium
composite panels is **IS 17682**, which covers panels for exterior and
interior use, including fire-retardant panels. The skin-to-core bond is
commonly assessed by a climbing drum peel test under **ASTM D1781**.

## Core types: the classification concept

Cores are broadly polyethylene (PE), fire-retardant (FR, mineral-filled) and
A2 (mostly mineral). The higher the mineral content, the less there is to
burn. Fire behaviour is expressed as a **reaction-to-fire class under
EN 13501-1**, derived from tests including the single burning item test
(**EN 13823**) and, for the A classes, heat of combustion (**EN ISO 1716**).
North American data often quotes **ASTM E84**, a tunnel test giving flame
spread and smoke indices; it is a different test and its results do not
translate into a Euroclass.

Two points matter more than the class names. The class belongs to the exact
product and thickness tested, not to "FR ACP" as a category. And a panel class
is not a facade verdict: the cavity, insulation and cavity barriers behind the
panel change how the wall behaves. The detail on FR, B1 and A2 cores is in
our [ACP fire rating explainer](/glossary/acp-fr-b1-core). What a particular
building requires is determined under **NBC 2016, Part 4** by the fire
consultant and the authority having jurisdiction.

## Coatings: PVDF vs polyester

**PVDF** (polyvinylidene fluoride) and other fluoropolymer coatings resist UV
and chalking and hold colour far longer outdoors. **Polyester** coatings cost
less and suit interiors and short-life signage, but fade and chalk sooner in
Indian sun. For exteriors, ask which performance standard the coating meets;
**AAMA 2605** is the highest of the AAMA organic coating classes for aluminium
panels. Metallic and mica finishes are directional, so every panel must be
installed with its arrow the same way.

## Fabrication, fixing and flatness

**Routing and folding.** A V or U groove is routed on the back, through the
back skin and most of the core, and the panel is folded along it to form a
tray. Routed too deep, the face skin cracks along the fold; too shallow, the
fold is rounded and the core fractures.

**Fixing systems.** Common systems are hook-on cassettes on pins (concealed,
single panels lift out), riveted or screwed flat sheets (visible fixings,
lower cost), and bonded systems (only with tested compatibility). The subframe
needs adjustable brackets and slotted holes so aluminium can move thermally. Panel size, thickness and fixing centres
follow from the design wind pressure under **IS 875 (Part 3)**, which is the
facade engineer's figure.

**Flatness and oil-canning.** Large panels in thin sheet, fixings
over-tightened, a subframe out of plane or restrained thermal movement all
show as waviness. Rear stiffeners, sensible panel sizes and a mock-up panel
viewed in raking light are the controls.

**Joints and sealant.** Open-joint cassettes behave as a rainscreen, draining
and ventilating the cavity. Sealed joints use a backer rod and a sealant that
must be compatible with the coating and non-staining, or light panels streak.

**Colour batch control.** Coil-coated colour varies between production runs.
Order each elevation from one batch, with spares from that batch for repairs.

## How it compares

Against high-pressure laminate, see [ACP vs HPL cladding](/compare/acp-vs-hpl-cladding).
Where fire performance, deep folds or absolute flatness govern,
[solid aluminium panel](/materials/solid-aluminium-panel) is the usual step up.
For a long-life natural metal finish, see [zinc vs aluminium cladding](/compare/zinc-vs-aluminium-cladding).
For how ACP sits within a full facade package, see the
[facade cladding systems](/services/facade-glazing/cladding-systems) service.

## Common mistakes

- **"ACP" specified without a grade.** Core, coating, skin thickness and
  standard are left open, and the cheapest sheet is quoted.
- **Signage-grade sheet on a facade.** Thin skins dent and oil-can; polyester
  fades.
- **Protective film left on for months.** Sun bakes it onto the coating.
- **Mixed colour batches** on one elevation, showing as a patchwork.
- **Arrows ignored** on metallic finishes, so adjacent panels read as different
  shades.
- **No single-panel removal.** One damaged panel means dismantling a run.

## What to ask your contractor or supplier

- Which core, and what is its tested reaction-to-fire class for this thickness?
- What skin thickness and coating, and which coating standard does it meet?
- Does the panel conform to IS 17682, and is there peel test evidence?
- What fixing system, and can single panels be removed?
- Open or sealed joints, and which sealant?
- How will colour batches and direction be controlled?

## Standards referenced

Aluminium composite panels under **IS 17682**. Reaction-to-fire classification
under **EN 13501-1**, with tests including **EN 13823** and **EN ISO 1716**;
surface burning characteristics under **ASTM E84**. Bond strength by climbing
drum peel under **ASTM D1781**. Organic coating performance under
**AAMA 2605**. Wind loads under **IS 875 (Part 3)** and fire and life safety
under **NBC 2016, Part 4**. The panel grade, fixing design and what any
building is permitted to use must be confirmed by the project's facade
engineer, fire consultant and the authority having jurisdiction.

## Frequently asked questions

### What is the difference between signage-grade and facade-grade ACP?

Mainly the skin thickness, the coating and the core. Signage and interior sheets often have thinner skins and a polyester coating, which is fine for a fascia or a partition but dents easily, oil-cans on larger panels and fades outdoors. Facade-grade sheet has thicker skins and a PVDF or similar exterior coating. The two can look identical on delivery, so the grade has to be written into the specification and checked on the delivered sheet.

### Which fire grade of ACP should be used on a building?

That is decided for each building, not by the panel catalogue. What the facade requires depends on height, occupancy and the rules at the site under NBC 2016 Part 4, and it is determined by the fire consultant and the authority having jurisdiction. The panel's reaction-to-fire class is a tested property of that exact product. Our ACP fire rating explainer covers what FR, B1 and A2 mean.

### Is PVDF coating worth it over polyester?

On an exterior, generally yes. A PVDF fluoropolymer coating holds colour and gloss far longer under Indian sun than a polyester coating, which can chalk and fade within a few years outdoors. Polyester remains a sensible choice for interiors and short-life signage. Ask which coating performance standard the coating meets, rather than accepting 'PVDF' as a word on a brochure.

### Why does an ACP facade look wavy?

That is oil-canning: visible waviness across a flat panel. It comes from panels that are too large for their thickness, uneven or over-tightened fixing, a subframe out of plane, or thermal movement that is restrained. Gloss and metallic finishes make it more visible. It is solved at design stage through panel size, stiffeners and subframe tolerance, and checked on a mock-up in raking light.

### Open joints or sealed joints: which is better?

They work differently. Open-joint cassettes act as a rainscreen: some water passes the joint and is drained and ventilated away behind, so the wall behind must be weatherproof. Sealed joints use a backer rod and sealant to keep water out at the face, but the sealant needs maintenance and can stain light panels if the wrong product is used. The facade designer chooses based on the wall behind and the maintenance plan.

### Can ACP panels be curved or folded?

Yes. Folding is done by routing a groove on the back, leaving the outer skin and some core, then bending along it to form cassette returns. Curves are formed by rolling within the manufacturer's minimum radius for that product and core. Very tight folds and complex three-dimensional shapes are where solid aluminium sheet is often the better material.

## Sources

- [IS 17682](https://standards.bis.gov.in/website/published-standards/department-wise) — Aluminium composite panel — specification
- [EN 13501-1](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Fire classification of construction products and building elements — reaction to fire
- [EN 13823](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Reaction to fire tests for building products excluding floorings — single burning item (SBI)
- [EN ISO 1716](https://www.iso.org/standards.html) — Reaction to fire tests for products — determination of the gross heat of combustion
- [ASTM E84](https://www.astm.org/products-services/standards-and-publications.html) — Surface burning characteristics of building materials
- [ASTM D1781](https://www.astm.org/products-services/standards-and-publications.html) — Climbing drum peel test for adhesives
- [AAMA 2605](https://fgiaonline.org/) — Superior performing organic coatings on aluminium extrusions and panels
- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/) — Fire and life safety
- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings and structures

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Source: https://hagerstone.com/materials/aluminium-composite-panel