Galvanised vs C5
"Standard galvanised" and "C5 coated" are the two SFS coatings you'll encounter on most UK projects. The difference between them is significant — in coating weight, cost, and the environments they're suitable for. This guide compares them directly, so you can specify the right one without paying for protection you don't need.
The basics — what "galvanised" means
Galvanising is the process of coating steel with zinc to protect it from corrosion. The zinc acts as a sacrificial layer — it corrodes before the steel does, protecting the steel underneath even if the zinc coating is scratched or damaged.
SFS studs and tracks are supplied galvanised. The question is not whether the steel is galvanised, but how much zinc coating it has. This is measured in grams per square metre (g/m²) of surface.
Higher coating weight = more zinc = better corrosion protection = longer service life = higher cost.
Coating weights compared
The zinc coating weight is the primary difference between standard galvanised and C5 coated SFS.
| Coating | Zinc Weight | Typical Specification |
|---|---|---|
| Standard galvanised SFS | ~100–140 g/m² | BS EN 10346 Z100 or Z140 |
| Heavy galvanised SFS | ~200–275 g/m² | BS EN 10346 Z200 or Z275 |
| C5 coated SFS | 275 g/m²+ | BS EN 10346 Z275 + additional coating (often zinc-aluminium) |
The exact specification varies by manufacturer, but the principle holds: standard galvanised is around 100–140 g/m², C5 is 275 g/m² or more. That's roughly 2–3× the zinc coating.
Service life compared
The service life of a galvanised coating depends on the corrosivity of the environment. In general, doubling the coating weight roughly doubles the service life before first maintenance.
| Environment | Standard Galvanised | C5 Coated |
|---|---|---|
| Dry internal (C1/C2) | 50+ years | Not required |
| Urban/industrial (C3) | 10–20 years | 25–40 years |
| Coastal/chemical (C4) | 5–10 years | 15–25 years |
| Severe (C5) | 2–5 years | 15–25 years |
| Extreme (CX) | Not suitable | 10–20 years |
These are rough figures — actual service life depends on the specific environment, coating quality, installation, and maintenance. But the relative difference is clear: C5 gives 2–5× the service life of standard galvanised in aggressive environments.
Environments compared
Where standard galvanised is suitable
- Dry internal environments (C1/C2)
- Heated and unheated buildings with normal humidity
- Internal partitions, ceilings, wall linings
- Protected soffits and canopies (not directly exposed)
- Anywhere the steel is within the dry envelope of a building
Where C5 is required
- Swimming pools and wet leisure facilities
- Coastal environments within 1km of the sea
- Marine and port facilities
- Chemical plants and refineries
- Food processing and wash-down areas
- Agricultural buildings with livestock
- Commercial kitchens and food prep areas
- Shower blocks and wet rooms
- External walls in industrial or coastal areas
- Chlorinated water facilities
- Sewage treatment facilities
- Anywhere with high humidity and chemical exposure
Where heavy galvanised might work
In some C3 environments — sheltered external, inland urban areas, some industrial settings — heavy galvanised (Z200 or Z275, without the additional coating of C5) may be sufficient. This is a middle-ground option that costs less than C5 but more than standard galvanised. Get advice from the manufacturer for specific environments.
Cost compared
The cost difference between standard galvanised and C5 coated SFS is significant:
| Coating | Relative Cost | Example (per metre) |
|---|---|---|
| Standard galvanised | 1× (baseline) | £1.00 |
| Heavy galvanised | 1.5–2× | £1.50–£2.00 |
| C5 coated | 3–5× | £3.00–£5.00 |
These are relative costs — actual prices vary by product, quantity, and supplier. The key point is that C5 costs 3–5× standard galvanised, and heavy galvanised costs 1.5–2× standard galvanised.
On a large project, the cost difference between standard and C5 can be tens of thousands of pounds. Specifying C5 unnecessarily is a significant waste; specifying standard when C5 is required is a serious risk.
Fixings and accessories
The fixings must match the coating of the SFS. This is critical — mismatched fixings become the weak point in the assembly.
| SFS Coating | Fixings |
|---|---|
| Standard galvanised | Standard galvanised or zinc-plated fixings |
| Heavy galvanised | Heavy galvanised or stainless fixings |
| C5 coated | Stainless steel fixings (A2 or A4 grade) |
Stainless steel fixings cost more than standard fixings, but they're essential for C5 applications. Using standard fixings on a C5 project is a false economy — the fixings will corrode faster than the C5 coating, and the whole assembly will fail prematurely.
Hybrid approaches
In some projects, a hybrid approach makes sense:
- C5 in wet zones, standard elsewhere — e.g. C5 for the shower block but standard galvanised for the corridor. This reduces cost without compromising the critical areas.
- Heavy galvanised instead of C5 — in C3/C4 environments where C5 is overkill but standard galvanised isn't enough.
- Additional protective coating — some projects apply an additional paint or coating to standard galvanised SFS to extend its life. This can work but adds labour and is generally less reliable than specifying the right coating from the start.
Hybrid approaches can work well but must be carefully specified — each zone must be clearly defined, and the transition points must be detailed correctly.
Decision guide
To decide between standard galvanised and C5 coated SFS, ask:
- What is the environment? Dry internal (C1/C2)? Sheltered external (C3)? Coastal or industrial (C4/C5)? Severe (C5/CX)?
- What is the required service life? 25 years? 50 years? Longer? Match coating to the target.
- What are the consequences of failure? Is this a low-risk partition or a critical infrastructure element? Failure in a swimming pool is much worse than failure in a corridor.
- What is the budget? C5 costs 3–5× standard galvanised. If the environment doesn't genuinely need C5, the cost premium is wasted.
- Is the specification clear? Don't leave it to the contractor to decide — specify the coating explicitly. "Standard galvanised" or "C5 coated" is unambiguous. "Galvanised" alone is not.
- Are the fixings specified? C5 needs stainless fixings. Specify both together.
If you're unsure, err on the side of asking. A quick call to the manufacturer or a technical consultant can save significant cost or prevent premature failure.
Summary
Standard galvanised and C5 coated SFS are the two most common coating options in UK construction. Standard galvanised is suitable for dry internal environments (C1/C2), covering most construction projects. C5 coated is required for the most aggressive environments (C5), including pools, coastal areas, and industrial plants.
The cost difference is significant — C5 costs 3–5× standard galvanised. Specify carefully: don't over-specify C5 for a dry internal wall, and don't under-specify standard for a wet or coastal environment. Match the coating to the environment, and match the fixings to the coating.
Key Takeaways
- Standard galvanised — 100–140 g/m² zinc, suitable for C1/C2 dry interiors
- C5 coated — 275 g/m²+ zinc, suitable for C5 (severe) environments
- Heavy galvanised — 200–275 g/m² zinc, middle-ground for C3/C4
- Service life roughly doubles with each doubling of coating weight
- C5 costs 3–5× standard; heavy galvanised costs 1.5–2×
- Match fixings to coating — stainless for C5, standard for galvanised
- Hybrid approaches can work — C5 in wet zones, standard elsewhere
- Specify explicitly — "galvanised" alone is ambiguous; specify the coating standard
Need help specifying the right coating?
Our technical team can advise on the right coating for your project environment — and save you money if C5 isn't actually necessary.