Aluminium does not rust. That is the headline benefit that makes it the material of choice for window frames curtain walls and architectural facades worldwide. But aluminium does something else: it corrodes.
Not in the red flaking way that steel rusts. Aluminium corrosion is subtler. It appears as white powdery patches a process called pitting or filiform corrosion that eats into the surface and over years compromises the structural integrity of thin sections. In coastal environments like Mogadishu where salt laden air is a daily reality that corrosion accelerates dramatically.
The difference between an aluminium facade that looks new after 15 years and one that looks tired after 5 years often comes down to a measurement most people never see: the micron thickness of the finish.
What Is a Micron?
A micron is one thousandth of a millimeter. Human hair is approximately 70 microns thick. The powder coating on an aluminium window frame is a layer of cured polyester or polyurethane resin typically between 10 and 20 microns thick that acts as the barrier between raw aluminium and the environment. That layer is thin. Invisible to the naked eye. But absolutely decisive in determining service life.
The Two Finishes: Anodizing vs Powder Coating
Anodizing is an electrochemical process that converts the aluminium surface into a hard porous oxide layer. It is extremely hard and has excellent UV stability but is limited in color range. Powder Coating applies dry powder electrostatically then cures it in an oven at 200°C. For most institutional applications in East Africa powder coating offers the best balance of aesthetics and availability.
A 10 micron powder coat is cheaper but it fails prematurely in coastal environments. A 20 micron coating provides a substantially more robust barrier.
Why 20 Microns Matters Especially at the Coast
Salt spray from the ocean deposits chloride ions on the aluminium surface. These ions are small and aggressive. They migrate through microscopic pinholes in thin coatings and initiate corrosion. Once corrosion starts it creeps under the coating lifting and delaminating it in thin worm like tracks.
A 20 micron coating ensures the path for chloride ions to reach the aluminium substrate is longer and more tortuous. Pinhole density is reduced and edge coverage is improved. We have observed and replaced 10 micron finishes on Mogadishu buildings that showed visible corrosion within 36 months of installation while 20 micron finishes remained unchanged.
How We Verify Finish Quality at Taslim
In our Nairobi fabrication facility we use two methods for verification. First an Eddy Current Thickness Gauge measures the distance to the substrate through the coating layer with an accuracy of 1 micron. Second we conduct Visual Inspection Under Magnification to ensure the coating has flowed properly around corners and into recesses.
Specification Checklist
When writing a specification insist on this language: All exposed aluminium surfaces shall receive a factory applied architectural polyester powder coating with a minimum average dry film thickness of 20 microns. For installations within 5km of the coast coating shall meet Qualicoat Seaside Class requirements.
At Taslim we build for the long term. That means sweating the microns.