What the designations mean: 304 (V2A) vs 316 (V4A) and their alloy composition
Stainless steel is a different family of steel from mild S235. What sets it apart is chromium, which forms a passive layer on the surface — a thin, self-repairing skin that resists corrosion. This is why stainless does not rust under normal conditions, even without paint.
Within that family, two grades matter for anything you hang outside.
V2A (AISI 304) is the standard grade for interiors and typical outdoor use. It carries chromium and nickel, and it holds up well in most gardens, courtyards and sheltered exterior walls.
V4A (AISI 316) adds one crucial element: molybdenum. That single alloy addition changes how the steel behaves near salt and chlorine. It is the grade you reach for when the air itself is working against the metal.
Both grades allow finishes that painted steel cannot: brushed and polished. Where a powder-coated panel is matte by design, stainless can carry a directional grain or a mirror-like face — the material becomes the finish.
The role of molybdenum in chloride resistance
The passive layer that protects stainless steel is strong, but it is not indestructible. Chlorides — the salts in sea air, poolside spray, road de-icing — attack it locally. Where the layer is breached and cannot self-repair, you get pitting: small, deep points of corrosion rather than uniform surface rust.
Molybdenum is what makes V4A more resistant to this attack. It reinforces the passive layer specifically against chloride pitting, which is why V4A is specified for coastal buildings, pools and marine environments while V2A is not.
Understand the limit honestly: stainless steel does not rust in normal conditions, but neither grade is invincible. Sustained chloride exposure and physical damage to the passive layer can still cause pitting over time. The choice between grades is a choice about how hard the environment will push.
Environment-based selection: inland, urban, coastal and pool areas
Match the grade to where the piece will actually live — not to a general idea of "outdoor."
- Inland gardens and sheltered walls: V2A (304) is appropriate. Rain, sun and frost are within its comfortable range.
- Urban environments: V2A generally suffices. City air carries pollutants, but chloride load is usually moderate away from salted winter roads.
- Coastal and seafront: V4A (316). Salt-laden air deposits chlorides continuously, and the molybdenum content earns its place here.
- Poolside and spa areas: V4A (316). Chlorine in the air is relentless, and this is exactly the load that pitting exploits.
The rule of thumb: if you can taste or smell salt in the air, or if chlorine is part of daily life at the wall's location, specify V4A.
Cost vs longevity: when V4A is worth the premium
V4A costs more than V2A because molybdenum and the higher alloy content cost more. The question is not which grade is "better" in the abstract — it is whether the premium buys you decades or wastes your money.
Inland, that premium is largely wasted. V2A will do the work, and the extra spend on V4A returns little you will ever see.
Coastal or poolside, the calculation inverts. Here, V2A is the false economy: a piece that pits and stains within a few years costs far more than the difference in grade. V4A is worth the premium precisely where the environment would defeat the cheaper grade.
This is a piece meant to outlast the moment it captures — the summit, the shoreline, the place that mattered. Buy the grade that lets it stay.
Specification checklist for outdoor installations
Before committing budget, work through this:
- Distance from the sea. Within a few kilometres of open salt water, default to V4A.
- Chlorine exposure. Pools, spas and covered water features push toward V4A regardless of coast.
- Winter road salt. If the wall sits near heavily salted roads, treat it as a chloride environment.
- Finish intent. Brushed or polished stainless shows its grade honestly; decide the look alongside the grade.
- Maintenance access. Rinsing salt deposits off periodically extends the life of either grade.
At Vestela, our current panels are powder-coated S235 and Corten — [do weryfikacji: czy Vestela oferuje panele ze stali nierdzewnej — obecna oferta paneli to S235 malowana proszkowo + corten]. For stainless specification and available sheet grades, [do weryfikacji: standardowa grubość i gatunek arkusza stali nierdzewnej u dostawcy CNC Vesteli].
