Aluminum was first used in the 1920’s for decorative detailing, and, then as now, hailed as a miracle material, because it won’t rust, it’s lightweight, and easily formed and shaped. By the 1930’s its uses expanded to structural components, facade coverings, railings, columns, and frames for doors & windows. Today, aluminum is recognized as one of the most sustainable construction materials. It’s long-lasting, practically maintenance free, and can be easily recycled into more new aluminum.
But, for a sophisticated, discerning, and evermore demanding customer-base, there’s a problem. It only comes in one natural color, silver-like, and because of the forces of Nature – sun, wind, acid rain, and air-borne salt – it won’t stay shiny. Though it will last virtually forever, it will exist with a pale, dusty looking film, that can’t be permanently polished away. In the worst climates such ‘natural’ exposure will eventually cause deep-surface corrosion. Customers don’t like that.
Enter the Coatings Industry. Answering the call, initially of high-end buyers, then everyone, the ‘industry’ now offers aluminum in a wide variety of coatings which come in almost any color including clear, and give corrosion resistance with a showy high gloss. It’s tough, long-lasting, and shiny. The problem is keeping it that way.
This is not about paint, like painting a room or a house, which involves paint being brushed, sprayed, or rolled-on on site. A coating is factory-applied to an already formed aluminum shape, then baked in an oven to achieve the right color, the right hardness, the right shine, the best protection against oxidation (a dusty film), and corrosion. By changing the baking time, temperature, and exposure, a variety of textures and finishes (like glossy or matte) can be achieved.
But, there are conditions which affect the quality of the application of coatings, most importantly thickness. For comparison, most coatings have a finished, dry-film thickness of barely 1.2 millimeters, while auto-industry standards range between 3.0 and 7.0 mils. For a thin film to protect against whatever Nature might throw at metal parts, like columns & posts, doors including sliders, hinges & handles, facades, gutters, railings, siding, thresholds, and windows, the consistency of the coating thickness is critically important. The more complex the part’s shape, the more broad will be the variation for film thickness.
Aluminum parts, other than some sheets, and forgings, are usually made as extrusions – molten aluminum is forced through a die, just like making shapes with children’s dough-clay. The coating is applied in several steps, such as a chemical dip or electroplating, followed by curing (hardening). The challenge is to assure that the thickness of the hardened dry film remains consistent all over the aluminum part. If the coating is too thick, it may not cure properly. Too thin, and protection against corrosion may be compromised.
SHAPE – Shapes like flat surfaces and rounded corners are easiest to coat correctly. More difficult are fins, blades, thin-edged plates, and deep vee’s. (illustration left). A good rule of thumb is: If it’s hard to see between extruded segments, then it’s also hard to coat in there to the right thickness.
EXPOSURE – Along with shape, exposure is just as important. Surfaces naked to the onslaughts of Earth might fade in color, and fail in finish. In spite of all man can do, Nature WILL win. Because film thickness may vary widely on such shapes as the inter-twinings of a filigree grill, and the deep facets of cast ornamental components, such items are more likely to show wear from weathering. Failure from such wear is not self-healing. Neither can repair be accomplished with spot-painting. It’s all or none. The entire part must refinished or replaced. Then the harsh force of weathering can begin again.
CLIMATE – The place of installation has full dominance over the life expectancy of coated aluminum. There are three primary zones :
1) Rural inland with low exposure to corrosive pollutants, and little to no salt; 2) Urban inland with high exposure to corrosive pollutants, and little to no salt; and 3) Coastal with high exposure to sun, wind, acid rain, wind-borne sand, pollutants, and LOTS of salt. Expected coating performance should at least resist the weathering conditions at the most extreme edge of any given climate zone.
…Exposure is most harsh in Zone 3, by the sea, but even more so when Zone 3 is hot. Whether arid or tropical, hot coastal environments encourage Mother Nature to combine every weapon in her arsenal, then release each in a withering succession of rapid fire attacks. Pollution, wind, rain, sun, sand and salt combine like a slow-burning nuclear bomb to degrade all parts of a home.
THE LESSON – This is NOT an indictment of the coatings industry. Far from it. The industry-wide efforts to cope with Nature’s unforgiving laws of physics are no less than heroic. This IS an admonition of caution to the public, at large, to choose metal parts and their shapes according to continuity of fabrication (simple shapes are better), as well as exposure to the elements of weathering, and the climate in which such exposure takes place.
CONSIDERATIONS FOR SUCCESS
- Make certain that suppliers and contractors consistently provide and install high performance products that can withstand the weathering within the selected climate zone for at least 10 years.
- Select simple shapes for ornamental details, railings, columns, opening trim, etc., with enclosed components (top, bottom, and ends), which will surround and protect any penetrations from connecting bolts & screws, and any attached and adjacent parts.
- Choose designs that minimize the number of cuts needed to fabricate individual components, which will help protect areas with potentially thin protective film. These could include designs with glass or metal panels, instead of traditional spindle-type designs.
- With professional assistance, examine the design for aluminum extrusions and details for complexity, and difficulty of a uniform coating application.
- Ask the same company which provides the aluminum units to do the installation. That company will have the most experience in situations involving potential damage during installation, as well as future repairs.
- Protect all coated components during shipping and storage, and after installation, prior to clean-up. Chemicals, like acid and bleach, used to clean building surfaces after construction is complete, can cause coatings to break down or weaken, thus shortening useful life.
ACTION TO TAKE – Railings and spindles, or any aluminum parts, with lots of architectural in’s & out’s will fail the fastest, killed by complexity. Simple shapes can be coated more evenly, and are more likely to last a very long time. Combinations of simple parts and pieces can yield the appearance of intricate detail. When it’s time to choose the adornments for your dwelling, be creative, but also be cautious and wise.
FINAL ACTION – Enjoy your home.