Summary
- Hot-dip galvanizing is highly effective for corrosion resistance, yet it leaves a heavy environmental footprint through chemical waste and high resource consumption that is hard to justify for steel products with a life cycle of only 15 years.
- The shot blasting & powder coating system is a three-stage steel surface treatment that combines shot blasting, an epoxy or zinc-rich powder primer, and powder painting for long-term corrosion protection.
- Shot-Blasted Powder Coating is an alternative to hot-dip galvanizing for most outdoor furniture.
- Shot blasting is particularly effective for steel products intended for powder painting, as it improves paint adhesion.
For products that are not intended for powder coating, we recommend hot-dip galvanizing for rust protection.
Steel products offer excellent longevity. At the same time, steel manufacturing is widely recognised as one of the more environmentally harmful industries. We constantly ask ourselves what is in our power to shift the balance towards sustainability without compromising our quality standards.
This question has led us to refine our approach to steel surface treatment for street furniture and outdoor steel products. You may have noticed that, alongside hot-dip galvanizing (HDG), we also offer an alternative, Shot-Blasted Powder Coating – a protection system based on shot blasting, an epoxy or zinc-rich primer, and powder coating. In this article, we explain how both methods work, what environmental impact they have, where each one performs best, and how to make the right choice.
Hot-Dip Galvanizing: The Gold Standard
For nearly two centuries, hot-dip galvanizing has been one of the most established methods of protecting steel against corrosion, weathering, and rust. It is widely used in bridges, railings, infrastructure, and industrial steel structures, as it provides robust, decades-long protection.
Nevertheless, hot-dip galvanizing comes with an array of disadvantages, with environmental impact being at the forefront. HDG relies on a series of chemical treatment stages. The process uses acids, fluxes, rinsing baths, and molten zinc heated to 450°C, all of which demand substantial resources and generate industrial waste. Without proper treatment, wastewater containing heavy metals and process chemicals can contaminate soil, groundwater, and living tissue. The galvanizing stage also produces zinc-containing dust and fumes that require industrial extraction to prevent their release into the environment and to protect workers. The process produces by-products such as zinc ash and zinc dross, which must be collected and managed as industrial waste. Much of the resulting by-product is classified as hazardous waste, which is impossible to recycle or regenerate.
Another challenge is ensuring paint adhesion to the galvanized surface. To achieve a reliable result, the surface often needs further abrasive preparation, such as sweep-blasting or sanding with a hand-held sander. If this preparation is carried out unevenly or too aggressively, the zinc layer can be thinned or damaged, which may reduce the quality of the final coating and affect long-term performance in damaged areas.
For this reason, while hot-dip galvanizing remains a suitable option in many cases, it is not always the most efficient or practical solution for every powder-coated steel product.
Shot-Blasted Powder Coating: Steel Surface Treatment Designed for Street Furniture
The shot blasting and powder coating system is a three-stage steel surface treatment that serves as an alternative to HDG. For quality control purposes, it is essential that all stages are carried out under one roof to ensure long-term corrosion protection and maximum coating adhesion.
For clarity, we use the term Shot-Blasted Powder Coating to describe the full process, which includes the following stages:
- Shot blasting: surface cleaning and adhesion
The first stage is shot blasting, where the steel surface is cleaned using small spherical steel shots propelled at high velocity in an enclosed chamber. This process removes mill scale, steel oxide, dust, and other residues from the surface. During blasting, the media is filtered, cleaned, and recycled for repeated use.
The result is not only a thoroughly cleaned steel surface, but also a microscopically textured profile created by the blasting media (size GH50). This surface profile significantly improves powder coating adhesion.
- Primer: corrosion protection
After shot blasting, either a zinc-rich or an epoxy primer is applied within a limited time window. This timing is important because it helps preserve the clean blasted surface and reduces the risk of oxide formation before coating. The selected primer forms the anti-corrosion base layer of the system and is an integral part of the overall protective coating build-up.
Unlike traditional galvanizing, which produces chemical by-products that can lead to heavy metal bioaccumulation in soil and living tissue, our dry shot-blasting and powder-priming system is entirely contained, preventing hazardous particulates from entering the ecosystem.
- Powder painting: finish and durability
Once the primer has been applied, a powder top coat is added in the desired colour. Both the primer and the top coat are applied as electrostatically charged powder, which is attracted to the steel surface and then cured in an oven, where the powder polymerises.
The result is a two-layer coating system, with approximately 70 microns per layer, delivering:
- a smooth and decorative finish,
- resistance to humidity and abrasion,
- and durable corrosion protection for outdoor use.
At Metalfabrik, all of these operations are carried out under one roof. This allows us to control timing, handling, and process consistency throughout the treatment cycle, which is important for achieving reliable quality and the intended product life.
Rethinking Hot-Dip Galvanizing
Compared with Shot-Blasted Powder Coating, hot-dip galvanizing is a multi-step process carried out off-site. It entails transportation to a specialised facility, chemical surface preparation, rinsing, fluxing, immersion in a molten zinc bath, and occasionally post-treatments such as passivation. These stages involve significantly higher use of chemicals and wet treatments. The steel must then be transported back to the manufacturing facility for the final step – powder painting.
For a product intended to serve for 15 years before being recycled, this can be an excessive process. While hot-dip galvanizing will protect a steel structure for many decades, both methods provide the necessary corrosion protection for street furniture in typical C3–C4 urban environments.
This leads to an important question:
“Are we using more protection than required?”
Best Use Cases
As with any process, each method is best suited to specific use cases.
Hot-dip galvanizing is a familiar, heavy-duty industrial finish widely used in large-scale structures and remains the go-to option for all furniture not intended for powder painting. Because a zinc-rich or epoxy primer only works in combination with a top coat, the primer alone cannot serve as a replacement for galvanizing if painting is omitted. We also encourage customers to opt for hot-dip galvanizing for street furniture subjected to direct impact, such as bike stands. When steel incurs deep scratches, galvanizing offers more robust protection against rust appearing in the damaged areas.
Shot-Blasted Powder Coating, on the other hand, is a more suitable technology for products with hard-to-reach spots and corners, where sanding prior to powder coating would be difficult to perform. That said, this technology requires precise implementation: selecting the appropriate blasting media, strictly controlling the timing between operations, and setting the correct parameters for polymerisation. At Metalfabrik, we meet these requirements by carrying out all stages of the process in-house, allowing us to maintain full control over every step and ensure consistent quality.
Ultimately, for most painted street furniture, we recommend Shot-Blasted Powder Coating, as it consistently delivers reliably good results.
While we always accommodate our customers by offering both options, we consider it our responsibility to inform and educate on limits and advantages of each treatment type. Our goal is to help you choose the protective coating that serves its purpose most meaningfully.
In our 20 years of steel manufacturing, we have invested significantly in R&D to develop new material treatment types, redesign product components and their assembly, and equip our factory with new technologies. By streamlining our production and keeping these processes in-house, we ensure a predictable result that fits the quality standards we are known for.
