South East Queensland is a hard environment for hardware. Subtropical humidity keeps surfaces wet for longer than a temperate climate does, the prevailing weather carries salt a long way inland, and a large share of the housing stock has a chlorinated pool within a few metres of the external hardware. Specify on price alone and you will see the result within a season.
| Material | Where it belongs | Where it fails |
|---|---|---|
| Zinc-plated mild steel | Interior, dry, conditioned space | Anywhere outdoors. The plating is measured in microns and is sacrificial — once it is consumed the steel underneath rusts. |
| Hot dip galvanised | Exterior structural, sheds, framing, fencing | Fine surface finishes — the coating is thick and rough. Not a substitute for stainless in salt spray. |
| 304 stainless (A2) | General exterior, inland and suburban | Direct marine exposure. It will not fail structurally, but it tea-stains. |
| 316 stainless (A4) | Coastal, marine, pool surrounds, anywhere washed in salt or chlorine | Nothing common in a domestic or light commercial setting. |
Both are austenitic stainless steels and both rely on a thin, self-repairing chromium oxide layer for their corrosion resistance. The practical difference is that 316 contains molybdenum, and molybdenum is what resists chloride attack specifically. Chloride is exactly what salt spray and pool water deliver.
Without it, 304 in a marine atmosphere suffers pitting and tea staining: rust-coloured streaking that runs down from the fastener. Tea staining is usually cosmetic rather than structural, but on a front entry door, a balustrade or an architectural handle it is the whole problem — nobody accepts a rust-streaked entry set on a new build.
Within roughly a kilometre of surf coast, or anywhere with a direct line to breaking water, and anywhere within a few metres of a pool or spa: 316. Further inland, sheltered, and not exposed to chlorine: 304 is generally adequate. Interior conditioned space: zinc-plated mild steel is fine and is a fraction of the cost.
Where a project is close to the line, or has an architectural finish that cannot be allowed to stain, specify 316. The material cost difference on a fastener is small next to the cost of replacing hardware on a completed job.
Put two dissimilar metals in contact with an electrolyte — and salt-laden moisture is a very good electrolyte — and the less noble metal corrodes preferentially. Stainless is noble. Almost everything you fix it to is not.
Cutting, grinding or drilling carbon steel near stainless hardware embeds iron particles in the surface. Those particles rust, and it looks exactly like the stainless has failed. It has not — but the stain is real and it is difficult to remove once it has bled. Keep grinding work away from installed stainless, and use dedicated stainless-only cutting and wire brushing tools.
Stainless is not maintenance-free; it is maintenance-light. The passive layer repairs itself in the presence of oxygen, but it cannot do that under a permanent film of salt. Anything sheltered from rain — hardware under an eave, on a covered balcony, inside a portico — never gets rinsed, and that sheltered hardware is consistently the first to stain. A rinse with fresh water a few times a year is the entire maintenance regime, and it is worth writing into the handover documents.
We stock both mild and stainless across the screw program, and stainless, steel, aluminium and PVC through the hinge and fittings programs. If you are specifying for a coastal project and want the grade confirmed against the line codes before you order, send us the schedule — we will mark it up.