When selecting painted panel facades, there are many considerations with long-lasting good looks that score high with asset owners and architects. However, the road to get there is not as simple as it initially seems. Is marine grade aluminum the pinnacle of the facade industry or a false hope?
As with all things in the building and construction industry, materials must be evaluated on their performance in the intended use situation before they are deemed “fit for purpose”.
Aluminum is no different, it has been the material of choice in the facade industry for many years, but the industry’s perception that “marine grade” aluminum must provide superior performance when used on painted aluminum panels should be reviewed.
Aluminum’s resistance to the harmful effects of corrosion relies on its ability to form its own protective barrier against oxides. The oxide barrier is a regenerative passive layer that protects the base metal from progressive corrosion. This basic ability of aluminum to resist corrosion varies between different grades; however, grades 3003 (widely used in architectural facades) and 5052 (marine) are among the best examples for corrosion resistance.
In heavy marine applications, where continuous exposure to the adverse effects of salt water is experienced, uncoated 5052 marine grade aluminum, in its raw form, will outperform the more conventional 3003 grade – that’s a fact.
But for architectural facades, where aluminum is clad, bent, and installed as curtain walls on buildings, the benefits of 5052 aluminum may be less obvious.
To challenge this idea, a 1000 hour neutral salt spray test was commissioned in accordance with AS 2331.3.1 and grades 3003 and 5052 were tested to determine which material came closest to meeting status. “Fit for Purpose” in painted architectural panels.
The test was conducted independently by Robert Jeffrey of Pacific Testing.
Two panels were prepared from roll coated aluminum, grooved and fabricated in a standard cassette format.
The surface of each panel was deliberately scraped down to bare metal, and the resulting reaction to the environment was observed and documented.
- Sample A: 3003 grade aluminum with primer and a single coat of PVDF
- Sample B: 5052 (marine) grade aluminum with primer and a single coat of PVDF
1. After 1000 hours, Sample A showed low level oxide streaking and blistering on the face of the panel and on the fringes emanating from the scratched areas. Sample B produced similar results with some low level blistering occurring on the panel.
2. Through the bend of the cassette, in areas affected by manufacturing, Sample A recorded low levels of blistering, while we saw high level blistering recorded on Sample B in several areas at through the elbow.
3. Looking at the cut edges, slight oxidation can be seen in Sample A along with low level blistering where water has migrated under the paint cut edges. Sample B shows signs of discoloration on bare sections, with no blistering.
Based on test results, 5052 Marine fails to provide a performance advantage over the widely accepted 3003 grade. Additionally, on sections where the substrate was mechanically fabricated (stamped and bent), the 3003 significantly outperformed the 5052.
If we are using this test to predict actual performance results on architectural facade applications, Grade 3003 should be considered a better “fit for purpose” base material.
We can conclude that although a low level of unsightly blistering may occur on cut edges, these are concealed by caulking/sealing joints and largely invisible. The bends in the cassette are however very visible and any corrosion seen here will destroy the overall appearance of the faceplate.
Why does 5052 blister fabricated areas?
The blistering we see is a direct result of poultice corrosion, which occurs when aluminum is exposed to trapped water in the absence of circulating oxygen. This can only happen if moisture finds a way under the surface of the protective PVDF coating.
What is the probable cause?
Under normal circumstances, it is the coating that provides weather protection and is the first line of defence. When the coating is compromised, we revert to the formation of an oxide layer to protect the aluminum from further degradation. But it is the formation of the oxide layer itself that compromises the appearance of the facade, breaking the bond of the coating and forming a surface bubble. In the oxygen-deprived bubble, poultice corrosion sets in and proliferates, while the protective oxide layer is unable to form in the absence of oxygen.
It has been widely documented that compared to the more flexible (feasible) 3003 grade, 5052 is prone to micro-cracking when bent beyond 90 degrees. Surface cracking of the aluminum can break the bond between the coating and the substrate, while allowing moisture to penetrate.
It is the coating and workability properties of the material of 3003 that make it best suited for use in architectural facades. Panels made of 5052 coated have a higher likelihood of being affected by bubbles caused by micro cracks and poultice corrosion.
Note: This is an internal review – FV provided both 3003 and 5052 samples used in testing