Richard Besant
is Director of Powdertech (Corby), a specialist architectural powder coater. Powdertech is a member of CAB (Council for Aluminium in Building) and ALFED (Aluminium Federation), and Richard is a member of the committee for EN 13438 – the European standard for powder coating on galvanised steel.
For specifiers and powder coaters of architectural aluminium, the recognised European Standard is BS EN 12206. Standards do not stand still and are revised in line with developments in technology and ongoing research. December 2020 will see the publication of the latest edition (BS EN 12206-1) after a long period of consultation. The benefit of the EU standards is that they have independent input from all interested parties, and the result is a practical standard that draws its information from a cross-section of the industry.
For those with a long memory, the original version of this standard was BS 6496 first published in 1984 and withdrawn in 2017 which meant that BS 6496 and BS EN 12206, which drew heavily from the text and tests of BS 6496, ran in parallel for 13 years, giving plenty of time for a transfer from one standard to another and ending any specification confusion.
Standards are not the most inviting of documents to plough through, so I thought it might be helpful if I took this opportunity to point out the significant changes in the latest standard, BS EN 12206-1:2020.
Equivalence in pre-treatment systems
This is the most significant stage in powder coating, and BS EN 12206-1 recognises the equivalence of the three more common processes broadly categorised as chrome-based, chrome-free and pre-anodised. Because BS EN 12206-1 is a performance-based standard and is not prescriptive as to the best pre-treatment process, it uses a range of performance requirements that must be met in order to meet the standard. It is worth noting that the use of chrome-based systems is likely to be phased out in the near future because of the proven carcinogenic and mutagenic effects associated with chrome.
Thickness of coating
Specifiers frequently ask “What is the correct film thickness” and “Is thicker better?”. BS EN 12206-1 addresses this in two ways. The minimum film thickness has been set as an absolute number, 40 microns. In addition, there is a recognition that different powders and different locations may need individual or local arrangements to achieve the performance requirement as set out in the standard. To answer the initial question, no, thicker is not always better.
Flexibility testing
Since the standard was first written, powder coating systems have improved significantly, resulting in the now common specification of Class 2 or super-durable products. These products have enhanced ultraviolet (UV) light performance for colour and gloss retention over an extended period of time though it should be noted that the specification of a Class 2 or super-durable product does not increase the corrosion resistance of the product.
There is a trade-off to this increased UV performance of super-durable products as the coating is less flexible.
BS EN 12206-1 recognises this with the establishing of Class A for the more flexible standard coatings and Class B for the super-durable coatings. The three coating flexibility tests on sample panels are: cupping (forcing a steel ball into a test panel), falling weight (dropping a known weight from a known height) and bend (bending around a mandrel). The use of the class rating is focusing the powder coating manufacturers on producing a better, super-durable product that combines enhanced UV stability with coating flexibility.
New pre-treatments
The final significant revision of the standard is the clarification of outdoor exposure performance requirements for “alternative” pre-treatments, including chrome-free, pre-anodising or other processes. This will ensure that all new pre-treatment systems have a clear performance target which allows product development without compromising performance.
A note of caution
Knowing the standard is not the same as knowing the performance. There are a number of aspects that specifiers should familiarise themselves with so there is a practical dimension to any specification.
Budget for the correct process as well as the colour
The relative cost between one colour and another may not be a major cost driver whereas, in the long-term, using the correct process is. It’s no use specifying for a fabulous colour if it peels off within five years.
Confirm your project corrosion category
A simple questionnaire confirming the location, elevation, distance from the seashore, prevailing winds and other factors will enable a powder coater to confirm the availability of a corrosion guarantee and the process required to achieve it. Look for notations C1 to C5 which define the corrosion features of that particular environment. Coastal locations are those closer than 2000m to the shore.
Class 1 and Class 2 powder products have no difference in corrosion protection properties
In most UK locations, a single coat of polyester powder of average thickness 60 microns will give excellent longevity. Discussing your needs with your powder applicator and powder manufacturer (preferably an approved applicator/manufacturer partnership) will result in the best practice. It is worth noting that use of either Class 1 or Class 2 products has absolutely no influence on the corrosion resistance of the system.
Pay attention to design detail
Design detail influences the performance of metal finishing in architectural applications. Design must address the corrosion category and powder coating process in order that its lifespan is not compromised. Such design aspects include the bends, folds, welds, gaps, edges, material gauge, recesses and fixing points of an architectural fabrication. For instance, sharp edges are corrosion origination points so need eliminating. Similarly, if material needs to be coated all over to achieve corrosion resistance, then the design must allow for this to happen.
Low maintenance is not ‘no’ maintenance
Finally, it makes sense to specify and design a system that supports a low-maintenance solution. This can be achieved by spending time at the start of the process so that initial and future cost can be quantified. For example, ensuring no water traps where salt can build up and initiate corrosion will add a known cost, whereas the future cost of repair and replacement is unknown.
The revisions to the powder coating standard BS EN 12206-1 will further enhance the reputation of this long-standing European Standard which specifiers should add to their library in the knowledge that it is supported by at least 21 other European and international standards, thus ensuring that it is both relevant and accurate.
In conclusion, in order to achieve the level of performance you and your client require from your powder coating, the finishing touch to the entire project, three critical factors will work together; engaging a powder manufacturer-approved applicator, spending time addressing the location and design details and referencing BS EN 12206-1 in the specification documents.
