Choosing the Right Metal Coating
A Simple Guide for Engineers & Buyers
Choosing the right surface coating can feel like navigating a maze.
Zinc flake?
Zinc phosphate?
Duplex systems?
Each process has its own strengths, specifications, and ideal use cases, but unless you live and breathe protective finishes, it’s easy to feel overwhelmed.
At Specialist Metallic Coatings, we believe technical decisions shouldn’t require guesswork.
Whether you’re an experienced design engineer or a first-time buyer, we make it simpler to get the right protection, first time.
Here’s a quick, no-jargon overview of our most in-demand coating processes, what they do, when to use them, and why they matter.
1. Zinc Flake Coatings
Best for: Fasteners, springs, clips, and components where high corrosion resistance without thread fill is essential.
Zinc flake coatings are water-based systems applied via Dip Spin or spray, offering exceptional corrosion protection (up to 1000+ hours in salt spray tests) without the risk of hydrogen embrittlement. This makes them ideal for high-strength steels and components where dimensional control is critical.
They’re also widely specified in automotive, rail and construction sectors for both aesthetic and functional finishes, often in silver, black, or grey variants.
2. Duplex Systems
Best for: Harsh environments, high-performance applications, and components needing both barrier and sacrificial protection.
Duplex systems combine two layers, typically a base layer (like electroplated zinc) and a topcoat (such as organic sealer or passivate), to deliver enhanced corrosion protection and improved wear or chemical resistance.
If your parts are exposed to aggressive conditions (marine, chemical plants, off-highway vehicles), duplex systems offer long-life protection that standard coatings can’t match.
3. Barrel Plating (Zinc, Zinc-Nickel)
Best for: High-volume small components that need economical, consistent coverage.
Barrel plating is a traditional but highly effective method for coating fasteners, washers, and fittings. At SMC, we operate fully automated lines for both zinc and zinc-nickel plating, ensuring uniform deposit thickness and controlled passivation.
Zinc-nickel is especially valuable when you need better corrosion performance than standard zinc, particularly in automotive and aerospace environments where longer warranties are expected.
4. Zinc Phosphate
Best for: Primer base for painting or powder coating, and applications requiring oil-retention or wear resistance.
Zinc phosphate is not a topcoat in itself, but a conversion coating that enhances adhesion and corrosion resistance of subsequent finishes. It’s widely used as a pretreatment in defence, construction hardware, and industrial applications.
It also has natural lubricity and can be combined with oils or waxes to reduce friction in moving assemblies.
5. Sherardising
Best for: Ferrous parts needing uniform, vapour-deposited zinc diffusion coating.
Although less common today, sherardising remains valuable for small, complex, or thread-sensitive parts, particularly in rail and utility infrastructure. SMC is one of the UK’s few remaining specialists offering this process, a nod to our rich technical heritage.
It provides a diffusion-based zinc coating that’s tightly bonded and extremely uniform, even on internal surfaces.
Choosing the Right Fit – With Support
Every project is different. What works for an exposed fastener may not suit a machined bracket. That’s why we don’t just offer coatings, we offer clarity.
Our team works closely with engineers, specifiers, and procurement teams to:
- Understand end-use requirements.
- Match specifications to budgets and timelines.
- Advise on compliance, recyclability, and finish appearance.
From early-stage consultation to final delivery, we ensure you’re not just protected, you’re well-informed.
Need Advice? Let’s Talk
Still unsure which coating is best for your application?
Let us help. Our team of specialists is on hand to guide you through the options and recommend a finish that meets your technical and commercial needs.
