The Fallacy of Marine Grade Aluminium in Facades

When selecting painted panel façades, there are numerous considerations, long lasting good looks scores highly with asset owners and architects, but the road to 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?

As with all things in the building & construction industry, materials need to be evaluated based on their performance within the intended usage situation before being deemed ‘Fit for Purpose’.

Aluminium is no different, 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.

LEARN THE DIFFERENCE BETWEEN ALUMINIUM GRADES HERE

• Sample A. 3003 grade aluminium with primer and single coat of PVDF
• Sample B. 5052 grade (marine) aluminium with primer and single coat of PVDF

Findings

1. After 1,000hrs, Sample A, recorded some oxide streaking and low-level blistering across panel face and on fringes emulating from the scratched areas. Sample B produced similar results with some low-level blistering occurring.
   
2. Across the Cassette Bend, in area effected by fabrication, Sample A recorded low levels of blistering. While we see high-level blistering being recorder on Sample B in several areas across the bend.
   
3. Reviewing the cut edges, mild oxidisation can be seen in Sample A and low-level blistering where water has migrated under the cut paint edges, Sample B has some signs of discolouration on the bare cuts, no blistering recorded.

Analysis

Based on the test results, 5052 Marine 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.

If we use this test as a predictor for real-life performance outcomes on architectural facade applications, the grade 3003 would have to be deemed as a better ‘Fit for Purpose’ base material.

We can conclude that while low level of unsightly blistering can occur on cut edges, these are concealed by caulking/sealed joints, and largely invisible. The cassette bends are however highly visible, and any corrosion seen here will destroy the overall look of the façade.

Why is 5052 blistering across fabricated areas?
The blistering we see is a direct result of poultice corrosion, poultice corrosion occurs when aluminium is exposed to trapped water in the absence of circulating oxygen. This can only happen if moisture finds a pathway under the protective PVDF coating surface.

What is the likely cause?
Under normal circumstances, it’s the coating that provides weather protection, and forms the first line of defense. When the coating is compromised, we revert to the formation of an oxide layer to protect the aluminium from further degradation. But it’s the formation of the oxide layer itself, that compromises the façade appearance, breaking the coating bond and forming a surface bubble. Within the oxygen deprived bubble, poultice corrosion takes hold and proliferates, while the protective oxide layer is unable to form in the absence of oxygen.

It has been widely documented that relative to the more flexible (workable) 3003 grade, the 5052 is prone to micro cracking when bent beyond 90 degrees. Surface cracking in aluminium can break the bond between coating and the substrate, while allowing moisture to penetrate.

Conclusion

It is 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.

*This is an internal review, FV sourced both 3003 & 5052 samples used in testing