Stainless steel in construction and architecture
Outdoors in construction, AISI 304 works; for interiors without moisture, 201 and 430 are enough, while in wet areas and by the sea 316L is needed.
The main mistake here is not in the grade but in the fasteners and the metal pairing: galvanised or aluminium fasteners paired with stainless steel trigger corrosion on the structure itself. Below — which grade is used where, which surface finish is chosen for a facade and an interior, and what is checked before purchase.
Where stainless steel is used in construction
| Element | Operating conditions | Grade | Surface |
|---|---|---|---|
| Facade cassettes and cladding | Atmosphere, rain, de-icing agents | 304 | 2B, №4, mirror |
| Roofing and drainage elements | Atmosphere, snow, moisture | 304 | 2B |
| Outdoor handrails and railings | Atmosphere, contact with hands | 304 | Brushed, polished |
| Indoor handrails and railings | Dry room | 201 | Brushed, polished |
| Fasteners and anchors | Outdoors, wet areas | 304, 316 for the sea | Uncoated |
| Frames, casings, brackets | Interior or outdoors | 201 indoors, 304 outdoors | Industrial, 2B |
| Decorative interior panels | Dry areas | 430, 201 | Brushed, mirror |
| Wet areas: bathrooms, kitchens | Water, detergents | 304, 316L | 2B, brushed |
| Swimming pools and damp areas | Chlorinated water, humid air | 316L, duplex 2205 | Brushed, polished |
| Load-bearing elements and cables | Load, atmosphere | 304, duplex 2205 | Industrial, 2B |
Sheet is used for cladding, cassettes, roofing and decorative panels. Profile pipe — for frames, railings and handrails. Angle and round bar — for embedded parts, brackets and fastening elements.
304 and 201: what is for outdoors, what is for interiors
The dividing line runs along moisture and contamination. 304 withstands the atmosphere, rain and anti-icing agents, so it is taken for all external elements: facades, entrance groups, handrails, roofing. 201 is cheaper because part of the nickel in it is replaced by manganese. This works in a dry heated room, but not outdoors: moisture and chlorides quickly show the difference.
430 is a ferritic grade without nickel. It is suitable for interior panels, casings and decor where there is no contact with moisture. It is not used in an urban atmosphere or in wet areas.
316L is needed where there are chlorides: swimming pools, sinks, coastal sites, car parks with de-icing agents, food and medical premises. Molybdenum in the composition is exactly what is responsible for resistance to chlorides.
On a facade in a coastal city or above a roadway with de-icing agents, even 304 requires care: contamination and salt deposits hold moisture on the surface, and corrosion starts under them, not on clean metal.
Surface finishes and architectural appearance
In construction, the surface finish solves two tasks: appearance and durability. A smooth surface retains less dirt and is easier to wash, a brushed one hides fingerprints and minor scratches, a mirror one gives an effect but requires care.
| Surface | Appearance | Where it is appropriate | Care |
|---|---|---|---|
| 2B | Matt, even | Facades, roofing, technical elements | Washing is enough |
| №4 brushed | A directional pattern | Handrails, entrance groups, panels | Wash along the brushing lines |
| Mirror, polished | Reflection | Accent elements, interiors | Regular polishing |
| BA | Light, smooth | Interiors, shop windows | Washing |
| Industrial, hot-rolled | Rough | Concealed structures | Not specified |
The direction of brushing on a facade is set in advance: a vertical pattern visually lengthens the building and does not collect dust the way a horizontal one does. The joints between sheets are turned so that the pattern matches — otherwise stripes will be visible on the plane.
Rigidity is a separate matter. A thin sheet over a large plane behaves like a membrane: it flaps when heated and in the wind. For facade cassettes, the thickness and the spacing of the brackets are selected, not just the grade.
Fasteners and the galvanic couple
Fasteners are the weakest point of a stainless steel structure. The rule is one: the fasteners must be from the same group of steels as the base metal, or more resistant than it.
- For 304, A2 or A4 fasteners are used; for outdoors by the sea, only A4.
- Galvanised, aluminium and black fasteners paired with stainless steel form a galvanic couple. What is destroyed in this case is the less resistant element, not the stainless steel.
- Contact with galvanised and aluminium structures is insulated with spacers.
- Fasteners in a wet area are not painted or lubricated with graphite.
- Concealed fasteners are checked for standing water: that is exactly where crevice corrosion begins.
Tools are monitored separately. A brush, a disc or a sling that has been used with carbon steel will leave particles of ordinary iron on the stainless steel. After a few rains they will produce rust spots that the customer will take for a defect of the grade.
After installation, external elements are inspected and treated: weld seams are cleaned and passivated, contamination is removed, the protective film is taken off within the period specified by the manufacturer.
Common mistakes
- Putting 201 outdoors. The economy grade in an urban atmosphere becomes covered with rust spots and loses its appearance within one season.
- Using galvanised fasteners. The galvanic couple accelerates corrosion, and then the fasteners are destroyed and the element loses its load-bearing capacity.
- Leaving the protective film in the sun. The glue under the film overheats and leaves marks that have to be removed by polishing.
- Storing stainless steel next to carbon steel. Particles of the foreign metal cause pitting rust on the surface.
- Ignoring seams after welding. Scale and the chromium-depleted layer become centres of corrosion, especially on a facade.
- Choosing the grade by the appearance of the sheet. 201, 304 and 316 do not differ visually but behave differently.
Frequently asked questions
Which stainless steel is suitable for outdoors
AISI 304 for most external elements. In coastal areas, near swimming pools and in zones with de-icing agents — 316L.
201 or 304 for outdoors
For outdoors — 304. 201 is suitable for interiors and decor; in a humid atmosphere it loses its resistance faster.
Which grade is needed for stainless handrails
Outdoors — 304, indoors — 201 or 304. In wet areas and by the sea — 316L.
Which fasteners to use for stainless steel
From the same group of steels: A2 for 304, A4 outdoors and in wet areas. Galvanised and aluminium fasteners are not used paired with stainless steel.
Which surface is best for a facade
2B or brushed №4. The mirror one is used for accent elements, because it requires regular care.
Can 430 be used outdoors
No. Ferritic 430 is suitable for dry interiors and decor; in the atmosphere it corrodes faster than austenitic grades.
Is passivation needed after installation
Yes, for weld seams and damaged areas. An untreated seam becomes the first centre of corrosion on a facade.
What to look at next
- Stainless steel sheet — thicknesses 0.8–10 mm and formats for cladding and cassettes.
- Stainless profile pipe — square and rectangular for railings and frames.
- Stainless angle — embedded parts and brackets.
- AISI 201: how it differs from 304 and where it is used — the limits of use of the economy grade.
Place an order
Choose the grade, size and surface in the catalogue of stainless steel products and place an order with the required shipment week. The delivery points in the buyer's and the seller's orders must overlap.