QUALICOAT Seaside Specification

The quality of any architectural powder coating relies on its ability to adhere to the aluminium substrate. If there is no ‘key’ to adhere to, the powder coating is prone to chipping or flaking off in use. As powder coating is porous at the molecular level, an untreated aluminium substrate, subject to weathering, will oxidise under the coating if it is not completely sealed. So, no matter the quality of the powder coating that is applied, it will not offer the anticipated life expectancy should the thin ‘conversion coating’, part of the pretreatment process which offers the seal and key to the surface of the aluminium, be poor, or indeed not present.

The surface of the extruded aluminium also carries contaminants from the extrusion process which, if left on the surface of the aluminium, will reduce the performance of the ‘conversation coating’ so this needs to be removed. Removing the contaminants from the extrusion is part of the pretreatment process undertaken by either dipping or spraying an acid or alkaline solution which etches the surface removing a minimum of 1g/sm of aluminium. Without this surface etch potential corrosion could form around the contaminants on the aluminium substrate once coating has been completed. Given that the pretreatment process is undertaken correctly, architectural powder coated products will offer an extensive life expectancy in most locations. The pretreatment process is actively monitored by members of the Association and third party inspected by IFO, QUALICOAT UK & Ireland’s independent test house.

Introduced in 2008, QUALICOAT also offer a ‘Seaside’ class of powder coating where the minimum removal of aluminium surface is increased to 2g/sm using a dip or spray process of either an acid or a combination acid/alkaline etch. This deeper etch removes more contaminants and therefore offers a more robust pretreatment for areas where atmospheres carry corrosive salts (chlorides) and other aggressive pollutants.

QUALICOAT licensed applicators who wish to offer ‘Seaside’ class coatings need to apply for an additional licence. The applicator needs to demonstrate that they can remove the 2g/sm by process and monitoring, plus the applicator must offer a coated ‘Seaside’ sample for an additional filiform corrosion test carried out in the IFO laboratory.

“To ensure coating sustainability, it is important that Seaside Class is specified for projects that are within 5km of the British coast or tidal estuary. Your systems supplier or powder coater can advise in more detail. You may find this link useful if you enter the postcode of your project location.”

Filiform corrosion, is a spider like corrosion that creeps under the powder coating and runs along the aluminium grain boundaries. A deeper acid or alkaline etching removes more trace elements from these areas making the grain boundaries more resistant to corrosion. The pretreatment conversion coating can then be applied using any of the QUALICOAT approved systems. Statistically, with this greater etch of 2g/sm, filiform resistance is increased significantly.

Another method of increasing resistance to filiform corrosion is by using a ‘pre-anodisation’ process, sometimes referred to as PREOX or Flash Anodising. A more expensive pretreatment, this thin anodising film of just 4-8 µm (microns) totally removes all the grain boundaries, so there are no places where filiform corrosion may take hold, consequently the protection rate is statistically increased to 100%. Licensed applicators may now source pre-anodised profiles from other licensed plants so that they may take advantage of the increased level of protection that this process can offer.

Technically, the QUALICOAT Specification is the most robust specification readily available in the UK & Ireland as it specifies minimum etch requirements within the pretreatment process for enhanced ‘Seaside’ applications and includes regular finished powder coated surface laboratory tests for filiform corrosion resistance, something which BS EN 12206-1 does not require.

QUALICOAT licensed members offering the ‘Seaside’ specification can display the Seaside logo above.