The Earth’s most abundant metal is renowned for its lightness, strength, and resistance to corrosion. And, for many at least, the silvery-white appearance of untreated aluminium extrusions is entirely adequate. All the same, there are many valid reasons to treat the surface of aluminium profiles. When using modular batten systems like Concept Click, aesthetic decisions are vital.
To name 5 of them:
- To introduce colour
- To supplement corrosion resistance
- To augment hardness
- To retard wear-and-tear
- To add reflectivity
Two coating systems are currently preferred when specifying architectural aluminium—anodised and powder coating.
Anodised and powder-coated aluminium
Anodising is the relatively straightforward electrochemical process, now nearly a century old, used to increase the thickness of the natural oxide layer on the surface of aluminum. (Aluminium oxide is a durable compound that seals and protects the base metal.) An example is shown below.
A technique chiefly used to apply decorative and protective finishes to aluminium, powder coating electrostatically charges the powder (a mixture of finely milled resin and pigment), sprays it on to the aluminium extrusion, and then fuses it into a smooth coating in a curing oven. An example is shown below.
Advantages of anodising
- Anodised aluminium is easy to maintain. Periodic cleaning with water and a mild detergent will restore its original lustre.
- The anodic coating will not peel or flake because it is actually part of the metal.
- Anodising imparts a translucent metallic appearance because the base metal can be seen underneath the coating.
- Anodising is unaffected by sunlight and therefore nearly fade-resistant.
- Anodised finishes are consistent regardless of the angle they are viewed from.
- Anodising does not emit volatile organic compounds (VOCs), nor are there any heavy metals involved in the process.
Disadvantages of anodising
- The surface of an anodised coating may become vulnerable to acidic pollutants in urban areas.
- The translucence of this coating contributes to color variation issues between batches, although this lack of uniformity has been reduced in recent times.
- Anodised finishes are normally only available in a matt and polished finish.
- Since anodised finishes can only be applied to aluminium, other building elements in a similar colour may look conspicuously different.
Advantages of powder coating
- Dents and scuffs are easily repaired using liquid coating that accurately matches original colours.
- Powder-coated aluminium installed at the start of a project will look the same as other powder-coated battens installed towards the end of the project.
- Powder coating is available in a huge range of colours (from simple matt, satin, and gloss finishes to super matt, super gloss, and textured finishes).
- Powder coating has better chemical resistance to mortar, as well as to industrial-strength acidic and alkaline cleaners.
- Powder coating has better colour uniformity between batches.
- Powder coatings do not produce air pollution.
Disadvantages of anodising and powder coating aluminium
- Filiform corrosion resembling threadlike filaments may form under the finish if incorrect pre-treatment methods are used.
- If the applied coating film is either too thick or thin, or if the powder coating material is too reactive, “orange peel” may occur.
- Chalking, which looks like white powder on the surface, may appear if the incorrect curing process is used.
- The very uniform and consistent coating makes the replication of the timber aesthetic, if so desired, unconvincing.
Whatever aluminium coating method you choose, it is crucial to select a reputable supplier with a proven track record in quality assurance at every stage of production, such as Interpon and Dulux (for powder coating) and GJames and AAF (for anodising).