When selecting painted panel façades, there are numerous considerations, long lasting good looks scores highly with asset owners and architects, but achieving this is not as straight forward as it initially appears. Is marine grade aluminium the shining pinnacle of the façade industry, or false hope?
Aluminium should be evaluated based on performance within the context of its intended usage before being deemed ‘fit for purpose’. It has been the material of choice within the façade industry for many years, but the industry’s perception that ‘Marine Grade’ aluminium must deliver superior performance when used on painted aluminium panels, needs to be reviewed.
Underpinning aluminium’s resistance to the detrimental effects of corrosion, is its ability to form its own protective oxide barrier. The oxide barrier is a regenerative, passive layer, that protects the base metal from progressive corrosion. This core ability of aluminium to resist corrosion does vary between different grades, however both the 3003 (widely used in architectural façades), and the 5052 (marine) grades, are some of the best-in-class examples when it comes to corrosion resistance.
In heavy marine applications, where continuous exposure to damaging effects of salt water is experienced, uncoated 5052 marine grade aluminium, in its raw form, will outperform the more conventional 3003 grade, it’s a fact. But for the purpose of architectural façades, where aluminium is coated, bent to shape and installed as curtain walls on buildings, the benefits of 5052 aluminium maybe less obvious.
To challenge this thinking a 1,000-hour, Neutral Salt Spray Test was commissioned, in accordance with AS 2331.3.1 and tested both 3003 and 5052 grades, to determine which material comes closest to satisfying the ‘Fit for Purpose’ status within painted architectural panels.
The test was carried out independently by Robert Jeffrey at Pacific Testing, where two panels were prepared from roll-coated aluminium, grooved and fabricated into a standard cassette format.
The surface of each panel was deliberately scratched down to bare metal, and the resulting reaction to the environment was observed and documented.
Based on the test results, 5052 fails to deliver a performance advantage over the widely accepted 3003 grade. Furthermore, on sections where the substrate was mechanically fabricated (routed and bent), 3003 significantly outperformed the 5052.
We can conclude that while a low-level of unsightly blistering can occur on cut edges, these are concealed by caulking or sealed joints, and are largely invisible. The cassette bends are however highly visible, and any corrosion seen here will destroy the overall look of the façade.
It's the coating and material workability properties of 3003 that make it best suited for use in architectural façades. Fabricated panels of coated 5052 have a higher likelihood of being adversely affected by bubbling caused by micro-cracking and poultice corrosion.
