Specifying & Maintaining Architectural Powder Coatings

by | Apr 10, 2024 | Viewpoint

By Angus Mackie – Qualicoat Chair

Powder coating was once seen as something that could be applied to aluminium to cover any irregularities, such as damage, corrosion, etc. Whilst this approach may allow the aluminium to look good for a few weeks or months after being coated, once weathered, the powder coating will quickly peel and fail. The reason for this is that powder coated finish is porous which allows moisture to reach the aluminium substrate where oxidisation will take place under the coating. Adhesion of the finish is also crucial and if the substrate does not offer a key, the powder coating can easily be chipped off. A quality pretreatment system is required if the powder coating is to offer a sustainable finish which can be maintained over several decades.

Often overlooked in the specification process, the pretreatment of the aluminium substrate is crucial as it has to firmly bond onto the aluminium. If the pretreatment is poorly applied, oxidisation of the aluminium over time can cause the powder coating to lose its adhesion. Licensed Qualicoat applicators across the globe are routinely inspected by independent test houses to ensure the latest Qualicoat Specification for pretreatment application is being followed.

Angus Mackie

Before any pretreatment system can be applied to the aluminium, the surface of the aluminium is cleaned of any surface greasy deposits from the extrusion process through an immersion or a cascade process. Following this the surface of the aluminium is then etched to remove surface contaminants in the aluminium. These processes ensure that the pretreatment system, bonds well with the aluminium substrate and once completed the profiles are oven dried prior to powder coating. It is important to note that the pretreatment system can be varied slightly to offer increased levels of protection.

The recently released Technical Information Sheet No.4 from Qualicoat ‘Recommendations for the Corrosion protection’ now offers specifiers guidance on the recommended pretreatment system to specify for various “Corrosivity categories” according to ISO 18768-1:2022 Table 1 and ISO 9223:2012 Table C.1. Whilst it is still strongly recommended that specifiers continue to seek guidance from a Qualicoat licensed powder coater or powder manufacturer when specifying finishes, the guide offers an insight as to the levels of protection offered when specifying Qualicoat architectural powder coating.

As with any applied finish exposed to British weather, it is important that a maintenance regime is undertaken to keep it performing and looking well for many years. Pollutants and airborne debris, which are deposited on powder coated finishes through weathering, can simply be cleaned down at the same time as window cleaning using mild detergent solutions. Aluminium window and facade longevity starts with a high quality aluminium substrate pretreatment and powder coat finish as provided by a licensed Qualicoat applicator.

Prior to handover of any new installation or building, coated aluminium fenestration will be cleaned down professionally to ensure that the finish is not damaged. It is crucial to have any areas of impact or abrasion damage repaired, should it be present. During cleaning, all the protective tape must be removed from the inside and outside of powder coated surfaces as if this is left on for an extensive time, the tapes low-tack adhesive can often degrade, especially in UV light, and become firmly attached to the powder coating.

Once handed over to the client, in normal use such as in cities, the powder coat finish should simply be washed down at yearly intervals with clean water or with a ph neutral mild detergent solution in water. This should be enough to protect the visible surface of the powder coat for many years and can simply be done during the cleaning of windows.  The powder coat finish wash down is especially important where squeegee bars are used to clean the glass, as their use tends to place the residue of the airborne contaminants directly on the powder coated frame which could begin to etch into the surface finish of the coating. Window cleaners must ensure that all powder coated surfaces are wiped clear of cleaning residue on every window clean.

On new and refurbished building projects, powder coated finishes will always come with a cleaning and maintenance regime from the company who coated the aluminium profiles. These will offer minimum cleaning requirements and need to be adhered to as well as being recorded when completed. This will ensure the coated finish is maintained within the applicators warranty and will help, should there be any claim in the future.  Warranties vary in length and are dependent on the powder coat finish used and the location of the installation. For example, where the coating is close to the sea, a Qualicoat ‘Seaside’ specification for the coating should be specified and the cleaning regime will often be increased to three-monthly intervals as the atmosphere is more corrosive.

Crucial to any maintenance regime is preventative maintenance and powder coating is no exception, if the coating in use has become damaged, exposing the aluminium, it should be repaired as soon as possible.  For repair, either contact the original coater, or approach any Qualicoat approved application who can normally offer guidance.

qualicoatuki.org

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