South Africa’s infrastructure is at a crossroads. With national priorities aligned towards expanding and maintaining critical rail, road, and harbour systems, the pressure on consulting engineers and specifiers to deliver cost-effective, durable solutions is greater than ever. As government agencies such as Transnet, the National Ports Authority, and SANRAL work to upgrade national infrastructure under tight capital expenditure constraints, the longevity of materials becomes a key consideration, especially in structures exposed to coastal or industrial atmospheres.
According to Simon Norton, Director of the International Zinc Association (IZA) Africa, one of the most effective ways to enhance the durability of steel structures is through hot dip galvanizing. “We must extend the operational life of steel and concrete infrastructure, particularly those within five kilometres of the coast or exposed to corrosive air pollution. Hot dip galvanizing offers a proven method to mitigate corrosion and improve asset longevity.”
Uncoated carbon steel, when exposed to the atmosphere, corrodes rapidly, especially in marine environments where salt-laden fog, mist, and wind carry aggressive contaminants inland. Even high-performance paint systems cannot provide indefinite protection, as microscopic pores and defects eventually allow moisture to penetrate and reach the steel beneath. By contrast, hot dip galvanizing applies a zinc coating that is metallurgically bonded to the steel surface.
This coating acts not only as a barrier but also as a sacrificial layer, meaning the zinc corrodes in preference to the steel, protecting the structural integrity over time. The corrosion rate of zinc varies across different South African regions and is well documented for engineering use, allowing for tailored design solutions. In reinforced concrete, hot dip galvanizing of rebar is also strongly advised to prevent internal corrosion and significantly extend the life of concrete infrastructure.
For roofing and cladding on infrastructure buildings, especially in rail and harbour environments, continuously galvanized steel sheeting is highly recommended. This material can be specified as zinc-coated steel with an organic primer and top coat or as aluminium-zinc (Galvalume®) coated steel with similar factory-applied finishes. These products are manufactured under strict quality standards and are commonly backed by warranties of up to 20 years by local suppliers.
Engineers working within five kilometres of the coastline should ensure that materials are rated for C5 environments, as per ISO 9223. Continuously galvanized sheet products used in roofing applications should meet the relevant standards, including SANS 4998, SANS 3575, EN 10346, and ASTM A653M. These standards ensure the product’s suitability for severe environmental conditions and long-term performance.
The quality of galvanizing is heavily dependent on the design and fabrication of the steel components. Components must be fabricated in accordance with SANS 14713, with welding preparation meeting the requirements of ISO 8501-3:2006. The actual galvanizing process should comply with SANS 121:2011 (ISO 1461:2009).
At the tender stage, a certificate of compliance, either via SABS (where applicable) or ISO 10474, should be requested to verify that the galvanizer adheres to industry standards. Coating thickness readings should be recorded and made available for each component. Additionally, all bolts used in construction, specifically grades 4.8 and 8.8, must be hot dip galvanized to SANS 121:2011 and overcoated with the same paint system applied to the structure for consistent protection.
Damage to zinc coatings can occur during handling and installation, but repairs are permitted under SANS 121 provided specific conditions are met. The maximum area for a single repair must not exceed 10 square centimetres, and the total repaired area must not exceed 0.5% of the component’s surface. Repaired coatings must achieve a dry film thickness (DFT) of at least 100 microns.
Several coating repair options exist, including brush-applied zinc-rich paints such as Zincdek 90 or Polygalv, which require multiple coats. Zinc-rich epoxies like Galvpatch and Zincfix are designed for single-application use and offer excellent coverage, with initial darker colours that fade over time to match the natural zinc patina.
When hot dip galvanizing is paired with a compatible organic coating, the result is known as a duplex system. These systems typically provide longer-lasting protection than either coating used independently, with performance improvements of up to 1.8 to 2 times the expected lifespan.
However, for duplex systems to perform effectively, proper surface preparation is essential. Galvanized surfaces must be cleaned of contaminants, including zinc oxides and residues from quenching baths. In fact, if painting is to occur post-galvanizing, it is critical that the galvanizer avoids applying post-treatment passivations or using contaminated water quenching processes. Paint adhesion failures are most often the result of inadequate preparation or incompatible coatings.
The best-case scenario is when the galvanizing and painting are handled by a single contractor, ensuring continuity in surface preparation and coating compatibility. If a third-party paint contractor is engaged, clear written communication must be provided to the galvanizer prior to the hot dip process.
Some galvanized steel components can be painted with little or no surface preparation, particularly items that are freshly galvanized (within 24 to 48 hours) or those that have weathered naturally in a rural environment for over a year. However, most components do not meet these ideal conditions and require rigorous preparation, especially those exposed to marine or industrial atmospheres. For this reason, IZA Africa strongly recommends appointing galvanizers with in-house painting capabilities or experience in managing duplex systems.
Galvanizing is not merely a protective measure, it is a strategic investment in the longevity and resilience of public infrastructure. By adhering to best practices in design, fabrication, and coating application, engineers can significantly reduce lifecycle costs, extend the service life of assets, and deliver infrastructure that stands the test of time.
As Norton puts it, “Galvanizing is not just about protecting steel, it is about safeguarding the integrity and value of our national infrastructure. The right coating choices today will define the reliability of our roads, railways, and ports for decades to come.”
