Aluminium Fenestration News

CHOOSE WISELY

By Angus Mackie – QUALICOAT UK & Ireland Chair

There are many powder coaters in the UK who can offer to powder coat virtually anything from outdoor street furniture to small engineering parts for a wide range of applications. These companies offer flexible coating and curing oven arrangements to meet a wide range of items that require finishing. Powder coating is becoming the finish of choice for many manufacturers as an alternative to volatile solvent based paints. Powder based coating is kinder to the environment, producing less harmful waste.

Products that are powder coated for internal use such as white goods, furniture and electronic products, will last a lifetime once coated. Products that are exposed to outdoor weathering require additional consideration.

Two standards in the UK relate to powder coating onto steel products, these are: ‘BS EN 13438:2013 Paints and varnishes – powder organic coatings for hot dip galvanised or sherardised steel products for construction purposes and ‘EN 15773:2018 industrial application of powder organic coatings to hot dip galvanised or sherardised steel articles [duplex systems] – Specifications, recommendations and guidelines’.

For powder coating onto aluminium, a different standard needs to be specified: ’EN 12206‑1:2021 Paints and varnishes.

Coating of aluminium and aluminium alloys for architectural purposes – Coatings prepared from thermosetting coating powder’. Whilst powder coating onto a galvanised steel substrate requires minimal pretreatment prior to powder application, aluminium requires a comprehensive pretreatment system to be applied. Powder coating for architectural purposes is normally applied to aluminium extrusion and sheet aluminium but can also be applied to aluminium castings.

An unfinished aluminium surface naturally oxidises and this oxide forms a protective layer against further corrosion. As powder coating is porous, any application of powder coating onto unfinished aluminium, which is exposed to the weather, will eventually begin to oxidise under the powder coating and as a result, over a period of time, the coating will lose it’s adherence to the aluminium. This will often be experienced as flaking of the complete coating revealing the aluminium underneath.

Whilst the thickness and quality of the powder coat application is important for a good life expectancy, a poor pretreatment of the aluminium will result in failure over time.

There are basically three recognised systems of pretreatment of aluminium, chrome based systems, chrome-free systems and a pre-anodisation process. Each of these systems involves an extensive investment in either wet dip immersion tanks or various spray booths where the process of cleaning, rinsing, etching, rinsing, pretreatment, rinsing and drying of the aluminium can take place. Once applied correctly, the pretreatment offers a complete seal of the aluminium surface and an important ‘key’ for the powder to adhere too.

Together with the investment in additional pretreatment plant for powder coating aluminium, powder coating to the EN 12206‑1:2021 specification requires careful calibration of the chemical pretreatment process and regular testing of the finished production. This requires a small laboratory facility together with a nominated Laboratory Technical to undertake and record these tests.

Possibly one of biggest perceptions with powder coating on aluminium is that it simply seals the surface and as long as it is applied in the correct thickness all will be OK. Well, for a short time it will be, but in the longer term, the finish will inevitably fail once exposed to the weather. Specifications for powder coated aluminium should always bear the EN 12206‑1:2021 standard as a minimum.

Ensuring this specification is on an order, should it not be complied with by the coater at least there is some recourse. By ‘choosing wisely’ a coater should be asked, and if possible visited, to ensure a robust pretreatment system is in place with a production testing facility.

Problems arise if the supply chain is not questioned or monitored. Where possible, aluminium systems such as doors, windows and curtain walls should preferably be coated as part of the aluminium systems company supply. If this is not possible, for example where several systems and fabricated cill/column pressings need to be accurately colour matched, one powder coater can be specified or nominated using a single batch of powder.

Whilst a specifier can request coating to EN 12206‑1:2021 and see the facility in the process being used correctly and in accordance with the standard? The problem is, architectural aluminium incorrectly coated can offer good adhesion for a few years before the coating begins to show failure. It is then often difficult to determine the absence of a quality pretreatment system and often very expensive to rectify.

A further standard, QUALICOAT, is well recognised across the globe and is independent of any nation being set up by powder coating companies themselves who wish to collectively raise the quality of powder coating. Established in 1986 with a head office in Zurich, QUALICOAT regularly update their standard following research and new developments. Copies of the QUALICOAT standard are freely available from the Association website.

At no additional cost to the specifier, a QUALICOAT specification, ensures that an architectural powder coater not only has the correct pretreatment plant and lab, but is working to a QUALICOAT specification. All QUALICOAT applicators carry a QUALICOAT licence and these are easy to check for on QUALICOAT’s own website. A licence is only offered to a powder coater when their facility, processes and testing regime meets the QUALICOAT standard. The standard encompasses EN 12206‑1:2021, and most importantly the powder coater is independently inspected by a third party, twice a year. Failing an unannounced inspection will mean that a QUALICOAT licensed applicator will lose their licence.

In the UK & Ireland many specifiers now recognise the importance of specifying QUALICOAT, indeed many of the UK & Ireland’s powder coaters are now QUALICOAT licensed and more powder coaters join each year. QUALICOAT remains a ‘global’ standard so a specification can confidently be made for any building in any country.

The global QUALICOAT standard continues to be incrementally revised with update sheets and a reprint of the standard every year. The standard is freely available for download at www.qualicoat.net. For details on the availability of various colours and finishes contact any QUALICOAT UK & Ireland member for more information. For updated information about the use and specification of QUALICOAT in the UK and Ireland, please visit the UK & Ireland Association website at www.qualicoatuki.org.

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