What you should know about marine grade aluminium on facades


When choosing painted panel facades, there are numerous considerations that score well with property owners and architects for enduring good looks. However, getting there is not as easy as it first seems. Is marine-grade aluminum the shining pinnacle of the siding industry, or a false hope?

As with all things in the building and construction industry, materials must be evaluated based on their performance in the intended use situation before they are considered “fit for purpose”.

Aluminum is no different, having been the material of choice in the cladding industry for many years, but the industry perception that marine grade aluminum must perform superiorly when used on painted aluminum panels needs to be reviewed.

Aluminum’s resistance to the damaging effects of corrosion is underpinned by its ability to form its own protective oxide barrier. The oxide barrier is a regenerative, passive layer that protects the base material from progressive corrosion. This core ability of aluminum to resist corrosion varies between different grades; However, both the 3003 (widely used in architectural facades) and 5052 (marine) grades are among the best in their class when it comes to corrosion resistance.

In heavy marine applications where it is constantly exposed to the damaging effects of salt water, uncoated marine grade 5052 aluminum in its raw form outperforms the more conventional 3003 grade – that’s a fact.

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But for architectural facades, where aluminum is clad, bent into shape, and installed as curtain walls on buildings, the benefits of 5052 aluminum may be less obvious.

To challenge this way of thinking, a 1,000-hour neutral salt spray test was commissioned to AS 2331.3.1, and both grades 3003 and 5052 were tested to determine which material achieved “Fit for Purpose” status in painted finishes construction panels.

The test was conducted independently by Robert Jeffrey at Pacific Testing.

Two panels were fabricated from roll coated aluminum, 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.

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

Results

1. After 1,000 hours, Sample A exhibited some oxide streaks and low level blistering on the panel surface and edges extending from the scratched areas. Sample B gave similar results with some low level blistering on the panel.

Panel face 1000 hours

2. Across the cassette bend, in areas affected by manufacturing, sample A showed minor blistering, while we saw sample B show severe blistering in several areas across the bend.

cassette curvature

3. Looking at the cut edges, Sample A shows slight oxidation along with some blistering where water has migrated under the cut paint edges. Sample B shows some evidence of discoloration on the bare sections with no blistering observed.

cutting edge

analysis

Based on test results, 5052 Marine offers no performance advantage over the widely accepted 3003 grade. Additionally, in sections where the substrate was mechanically processed (milled and bent), the 3003 significantly outperformed the 5052.

If we use this test to predict real-world performance results in architectural facade applications, grade 3003 would have to be considered a better base material for the purpose.

We can conclude that while a small degree of unsightly blistering can occur at cut edges, these are hidden by caulking/sealed joints and are largely invisible. However, the coffer bends are clearly visible and any corrosion seen here spoils the overall look of the facade.

Why does 5052 bubble in the crafted areas?

The blistering we see is a direct result of envelope corrosion that occurs when aluminum is exposed to trapped water in the absence of circulating oxygen. This can only happen when moisture finds a way under the protective PVDF coating surface.

What is the likely cause?

Under normal circumstances, the coating is the weather barrier and the first line of defense. When the coating is compromised we revert to forming an oxide layer to protect the aluminum from further degradation. But it is the formation of the oxide layer itself that spoils the appearance of the facade, breaking the coating adhesion and forming a surface blister. Within the oxygen-poor bubble, pock corrosion settles and spreads, while the protective oxide layer cannot form in the absence of oxygen.

It has been well documented that grade 5052 is prone to micro-cracking when bent more than 90 degrees compared to the more flexible (machinable) grade 3003. Surface cracks in aluminum can break the bond between the 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 facades. Panels manufactured from coated 5052 have a higher likelihood of being affected by blistering caused by microcracking and compressive corrosion.

Please note: This is an internal review – FV sourced both 3003 and 5052 samples used in the tests



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