The global powder coatings specification for powder coating over aluminium now in its 14th Edition has its strength in the ‘triple lock’ approval system, firstly, the pretreatment chemistry, secondly the application process, and thirdly the powder used, where for each of these three elements independent approval and inspection is required. For the vast majority of architectural applications, the standard QUALICOAT approved one coat system is perfect, where the strength of weathering is identified by the Class of powder chosen.
BUT there are a few occasions where real consideration can be given to the effective use of two coats. QUALICOAT, in recognition of these developments has now approved a number of excellent two coat systems, these can be seen on the approved powder systems list at www.qualicoat.net
“So, why two coats!”, I hear the refrain. “Is this a ruse by the industry to charge more for powder coating?”. Well…..no.
Two coats, or multi coat systems have been available in the paint industry from the beginning, starting with wet paints. Powder coatings from their inception have penetrated the paint market well often on economic grounds as it is an effective one coat system. For powder coatings, as the technology has improved the use of multi coat systems has become more common place typically for industrial purposes over steel e.g. for plant, machinery and equipment.
For the architectural world for powder coating over aluminium a ‘two coat system’ maybe relevant in specific circumstances. What might these be?
The corrosion class of the environment where the building is located is the main consideration, followed by the material to be coated, and then from a commercial point of view, for the warranty period to be offered.
Environmental corrosion classes from C1 to C5 are outlined and described in ISO12944-2, where C5 is the most corrosive environment.
In more challenging environments (C4/C5) certain aluminium materials and fabrications may be more susceptible to corrosive attack.
Let us consider perforated aluminium sheets. Probably the weakest area for any paint finish is the sharp edge. Sheets have 4 sides and potentially 4 sharp edges. A perforated aluminium sheet additionally has 100’s of punched, sharp perforations. This multiplies the risk areas considerably.
QUALICOAT is a specification label and is not involved in such considerations. The approved applicator however and the approved powder supplier are the parties who offer warranties. Where a location is hazardous; where the coated part is challenging; where a long period warrant is required, a two coat system will help.
Two coats provide an additional barrier to the negative weathering effects of UV light, temperature and moisture. And a two coat system can provide superior edge coverage. For these reasons, an applicator who chooses an approved QUALICOAT two coat system may have more confidence in the warranty period to be offered after discussion with their powder supplier.
Two coat systems over aluminium are gathering traction and have a role to play in the armoury of QUALICOAT approvals designed to better tailor the finish quality to the clients’ requirements.
QUALICOAT remains one of the leading specifications because it evolves its approvals and tightens its limits with the 15th Edition due for release later this year. All designed to provide reassurance to the client. Quality and consistency of quality, continues to be highlighted by the association which includes third party testing of all certified powder formulations and pretreatment systems that make up the QUALICOAT approval process. For specification support, any member of the association can offer advice and guidance. For updated information about the use and specification of QUALICOAT in the UK and Ireland, please visit the associations’ website at www.qualicoatuki.org