A specifier asks: "Is stainless steel always the right choice for a hospital door?" The honest answer is no. Grade 316 stainless in a dry administration corridor is money spent for zero performance gain, while cold-rolled steel with a poor coating system in a damp sterilisation area will show rust bleed within two years. Material selection is a question of matching environment to substrate — not of buying the most expensive option.

12.1 The four candidate materials

Cold-rolled steel (CRS). Smooth surface, tight tolerances, good strength — the default substrate for painted interior doors. Its weakness is that it has no inherent corrosion protection: the entire defence is the coating system on top of it. Once a scratch reaches bare metal in a humid or chemically cleaned environment, underfilm corrosion starts and spreads invisibly under the paint.

Galvanized steel. CRS with a zinc coating (hot-dip galvanized or electro-galvanized). The zinc protects sacrificially — even at cut edges and small scratches, zinc corrodes preferentially and shields the steel. This is why galvanized is the preferred substrate for powder-coated hospital and cleanroom doors: the zinc is the corrosion insurance, the powder coat is the hygienic, cleanable surface. Electro-galvanized gives a smoother finish for coating; hot-dip gives a thicker zinc layer and better long-term protection.

Stainless steel (304 / 316). Corrosion resistance comes from the chromium-rich passive layer in the alloy itself, not from a coating — scratches do not trigger spreading rust. Grade 304 suits most healthcare interiors. Grade 316 adds molybdenum and resists chloride attack: it is the correct choice for coastal sites, wet processing areas and frequent aggressive disinfection. Trade-offs: 2–4× the material cost of galvanized, harder to fabricate (work hardening, lower thermal conductivity when welding), and it shows fingerprints — brushed (No. 4) finishes mitigate this.

Aluminium alloy. Light (roughly one-third the density of steel), naturally corrosion-resistant, easy to extrude into complex profiles. Limitations: lower strength and stiffness (needs thicker sections or reinforcement), poor performance in fire-rated doors (aluminium loses strength rapidly above ~200 °C), and surface softness — anodising or powder coating is needed for durability in high-traffic use. Common for cleanroom window frames, lightweight sliding leaves and hermetic door panels where mass matters for operators.

12.2 Comparison table

Property Cold-rolled steel Galvanized steel Stainless 304/316 Aluminium alloy
Strength / stiffness High High High Low–moderate
Corrosion resistance None without coating Good (sacrificial zinc) Very good; 316 resists chlorides Good (natural oxide)
Behaviour when scratched Rusts, creeps under coating Zinc still protects edges Passive layer self-repairs Oxide self-repairs
Fabrication Easy to weld/form Easy; venting needed when welding HDG Harder; work-hardens Easy to extrude; welding needs care
Fire-rated door suitability Good Good Good Poor
Maintenance Repaint damaged areas Low Very low; clean and passivate Low
Relative cost 1.0 (baseline) ~1.1–1.3 ~2.5–4 ~1.5–2.5
Typical medical use Painted interior doors Powder-coated hospital/cleanroom doors Operating theatres, wet labs, coastal sites Hermetic sliding doors, lightweight leaves

12.3 Common mistakes

  • Specifying stainless everywhere "to be safe" — the budget would buy better hardware and seals, which fail more often than door skins.
  • Painting bare CRS in wet areas — any chip becomes a corrosion site; use galvanized substrate under the coating.
  • Ignoring cut edges — laser-cut and punched edges of galvanized sheet lose some zinc protection; good manufacturers treat or seal them.
  • Mixing metals carelessly — stainless fixings on galvanized doors are fine; the reverse (carbon steel fixings on stainless) causes rust staining.

Practical recommendation

Default to electro-galvanized steel with a quality powder coat for general hospital and cleanroom doors. Reserve stainless 304 for operating theatres and high-disinfection zones, 316 for wet/chloride exposure, and aluminium for lightweight or hermetic sliding leaves. Use CRS only in dry, low-risk interiors.