Powder Coating - What Should I Specify?
Architects specify powder coating for the majority of their projects for use in the external envelope, but what should they specifically ask for by way of specification clauses?
The size of the project can often have implications of what detail is entered into when it comes to powder coating. If the project is just a pair of doors or a few windows, normally only the colour will be referred too and possibly the gloss level. But if the project is significant then often architects will either employ a powder coating consultant or rely on the sub-contractor to get the coating correctly supplied, with the latter solution potentially leading to problems further down the project time-line.
Architectural powder coating is a two step process; the cleaning and pretreatment of the aluminium and then the powder coating itself. Only when both processes are correctly done, with suitably sourced materials for the location of the project, can the project be deemed to offer a sustainable powder coating solution.
To add to the mix, projects often carry not just extrusions but preformed sheet pressings cills, preformed column casings and often aluminium sheet used in composite spandrel panels. These are often powder coated in differing locations which can introduce shading issues between batches, or indeed manufacturers of different powders. To further complicate matters should aluminium castings need to be coated, these may be coated in a further coating facility. The key to success is to discuss the finishes of various suppliers of materials and ideally have everything powder coated by the same powder coater if possible.
If this scenario is not going to be possible, quality control can be achieved by recognising what the variations in finish might be acceptable by agreeing up front both the colour variance and gloss variance on the proposed finish. The main issue is that being prepared for potential colour variation meant that this could be potentially controlled to a degree to minimise its effect.
Is it important to choose which company is going to powder coat profiles for a project?
If the architect is specifying a known systems company for their project it is often best to allow the systems company to powder coat the profiles, or indeed allow them to specify who they use. Guarantees for coatings quality often then are passed onto the end user through the systems company who take responsibility for both the profile and coating quality. It is crucial however to note this within any specification so potential future issues can be easily rectified through the right channels.
In the UK and Ireland, independently licensed, quality powder coating is provided by members of QUALICOAT. A global organisation offering a common standard. The Association recognises the need for both quality pretreatment systems, quality finishing powders and the quality in the finish applicators. The association therefore licences both producers of the materials and applicators to ensure that quality levels are attained and maintained. Regular inspection of QUALICOAT licence holders are undertaken by third party test houses and should failures in processes be recognised then QUALICOAT licences could be withdrawn. This is a crucial cornerstone of the association to ensure members offer the highest level of quality for all their production output.
For pretreatment or the conversion coating of the aluminium, either a chrome free or chrome based system can be used for most locations. The aim of this pretreatment is to completely seal the aluminium substrate to stop oxidisation. Alternatively, a thin anodised finish can be used prior to powder coating which offers a more robust pretreatment. There are also variations of pretreatment options when is comes to specifying projects near the cost when a ‘Seaside’ class of pretreatment can be used which incorporates a longer or deeper aluminium etch process to remove substrate contaminants.
Powders also come in various grades, all offer a long life expectancy, but higher grades, or classes of powder offer greater colour fastness when subject to UV light and better gloss retention. Gloss can be lost as a result of airborne abrasion as well as UV degradation. Typically, we see Class 1 powders used in the UK with some high rise and prestigious projects opting for more resilient Class 2 powders. Class 3 powders are generally not used in the UK and are specified in harsher environments such as in the equatorial regions.
There is quite a mix to choose from and the recommendations from QUALICOAT to the Specifier would be to review the various providers of coated aluminium in the facade, even if it is coming from just one installer/sub-contractor. By being aware of the potential issues that could be raised on what is the most visible aspect of an aluminium facade, its finish is crucial to a project being completed on time and in the right quality.
QUALICOAT members, who can be found on the QUALICOAT UK & Ireland website, are available to discuss any project requirements and advise on the best combination of pretreatment and powder coating for any project given its location and exposure.
The sixteenth edition of the QUALICOAT Standard, is available through the UK Association website, www.qualicoatuki.org together with an up-to-date list of licensed Powder Suppliers, Pretreatment Suppliers and Applicators. Printed literature and telephone support is available from QUALICOAT UK & Ireland Head Office in Birmingham on 0330 236 2800 or email firstname.lastname@example.org. The Association can also be followed on Twitter @Qualicoatuki
QUALICOAT UK & Ireland with offices based in the Midlands is the National Association for QUALICOAT approved companies. QUALICOAT is a global quality label organisation committed to maintaining and promoting the quality of lacquering, painting and coating on aluminium and its alloys for architectural applications.
Please browse our website and should you have any questions about architectural powder coatings and the correct specification, please contact one of our local members or phone our office on the number below.
QUALICOAT UK & Ireland Chairman