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.

By Dhruv Agarwal · · 5 min read

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

LayerWhat it doesWhat to specify
Face coatingColour, gloss and weathering lifeCoating type (PVDF, FEVE or polyester) and the performance standard it meets
Face skinStiffness, dent resistance, flatnessAlloy and skin thickness, from the manufacturer's data
CoreBonds the skins; decides fire behaviourCore grade with the tested reaction-to-fire class for that product and thickness
Back skinBalances the panel so it stays flatSame alloy family, with a service coat
BondHolds skins to core over the panel's lifePeel strength test evidence
Protective filmProtects the face until installationRemoval 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. 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. Where fire performance, deep folds or absolute flatness govern, solid aluminium panel is the usual step up. For a long-life natural metal finish, see zinc vs aluminium cladding. For how ACP sits within a full facade package, see the facade 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.

Standards referenced

  • IS 17682 — Aluminium composite panel — specification (Bureau of Indian Standards)
  • EN 13501-1 — Fire classification of construction products and building elements — reaction to fire (CEN-CENELEC)
  • EN 13823 — Reaction to fire tests for building products excluding floorings — single burning item (SBI) (CEN-CENELEC)
  • EN ISO 1716 — Reaction to fire tests for products — determination of the gross heat of combustion (ISO)
  • ASTM E84 — Surface burning characteristics of building materials (ASTM International)
  • ASTM D1781 — Climbing drum peel test for adhesives (ASTM International)
  • AAMA 2605 — Superior performing organic coatings on aluminium extrusions and panels (Fenestration and Glazing Industry Alliance)
  • NBC 2016, Part 4 — Fire and life safety (Bureau of Indian Standards)
  • IS 875 (Part 3) — Wind loads on buildings and structures (Bureau of Indian Standards)

Frequently asked

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.

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.

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.

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.

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.

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.

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