Woodform Architectural evaluates the most suitable coating systems for aluminium profiles by examining their advantages and disadvantages.
Aluminium is one of Earth’s most abundant metals known for its lightness, strength and resistance to corrosion. Untreated aluminium extrusions are perfectly adequate for many applications; however, there are many valid reasons to treat the surface of aluminium profiles. These include introducing colour, supplementing corrosion resistance; augmenting hardness; arresting wear-and-tear; and adding reflectivity.
Two coating systems – anodised and powder coating – are currently preferred when specifying architectural aluminium.
Nearly a century old, anodising is a relatively straightforward electrochemical process used to increase the thickness of the natural oxide layer on the surface of aluminium.
Powder coating, on the other hand, is a technique mainly used to apply decorative and protective finishes to aluminium profiles through a process that electrostatically charges the powder consisting of a mixture of finely milled resin and pigment, spraying it on to the aluminium extrusion, and then fusing it into a smooth coating in a curing oven.
Advantages of anodised coatings
Easy to maintain, anodised aluminium can be cleaned periodically with water and a mild detergent to restore its original lustre. Being part of the metal, the anodic coating will not peel or flake and also imparts a translucent metallic appearance. Anodising is unaffected by sunlight preventing fading, and does not emit VOCs. There is no use of heavy metals in the process.
Disadvantages of anodised coatings
Anodised coatings may become vulnerable to acidic pollutants in urban areas. The translucence of the coating may lead to colour variation issues between batches, although this lack of uniformity has been reduced in recent times. Anodised finishes have a limited range of options and 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 coatings
Powder coating is a highly versatile aluminium surface treatment option and offers several advantages in any application. For instance, 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. Consistency in finish is assured with powder-coated aluminium installed at the start of a project looking the same as other powder-coated surfaces installed towards the end of the project.
Dents and scuffs are easily repaired using liquid coating that accurately matches original colours. Powder coating has better colour uniformity between batches. Offering excellent chemical resistance to mortar, as well as to industrial-strength acidic and alkaline cleaners, powder coatings do not produce air pollution.
Disadvantages of anodising and powder coating aluminium
Incorrect application of anodised and powder coatings can result in unsatisfactory outcomes such as filiform corrosion resembling threadlike filaments forming under the finish; occurrence of orange peel if the applied coating film is too thick or thin, or if the powder coating material is too reactive; and chalking, which looks like white powder on the surface, appearing due to incorrect curing.
Being very uniform and consistent, powder coating will not be able to replicate the timber aesthetic convincingly.
Most importantly, regardless of the chosen aluminium coating method, a reputable supplier must be chosen 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).