- 304 is the correct default for interior food-grade work.
- Move to 316 for chlorides: coastal air, pool plant, heavy sanitiser.
- Grade never rescues a bad detail. Crevices corrode in any grade.
Almost every quote we issue involves this decision, and almost every time the client has already been told by somebody that they need 316. Sometimes that is true. More often it adds thirty per cent to a material bill for a corrosion risk that does not exist in a Parramatta kitchen or a warehouse in Western Sydney.
Both grades are austenitic stainless steels and both rely on the same mechanism: enough chromium to grow a passive chromium-oxide film that heals itself when it is scratched. The difference is that 316 adds around two per cent molybdenum, and molybdenum is what keeps that film stable when chloride ions are attacking it.
The test we actually apply
Ignore the marketing language about marine grade and ask one question: will this surface see chlorides, and will they be allowed to sit there? Chlorides come from salt air, from pool and spa plant, from bleach and quaternary sanitisers, and from food waste that is left on a surface overnight. If the answer is no, 304 is not a compromise. It is the right specification.
| Environment | Grade | Why |
|---|---|---|
| Interior kitchen benches and sinks | 304 | Washed daily, no standing chlorides |
| Exhaust canopies and flue | 304 | Heat and grease, not salt |
| Coastal site within ~1km of surf (Bondi, Manly, Gold Coast) | 316 | Airborne chloride deposition |
| Pool plant rooms and wet areas | 316 | Chlorinated atmosphere |
| Cool room floors and drains | 316 | Standing water, aggressive cleaning |
| Structural framing behind cladding | Mild steel | Coating carries the corrosion duty |
Where grade does not help you
Crevice corrosion does not care what you paid for the sheet. If two surfaces are lapped and sealed with silicone instead of welded, moisture wicks into the joint, oxygen cannot reach it, and the passive layer cannot rebuild. That joint will fail in 316 as surely as in 304. It will just take a little longer.
- Lapped and sealed joints instead of fully welded ones.
- Carbon steel contamination from a grinder that has been used on mild steel.
- Weld heat tint left unpickled, where the chromium has been drawn out of the surface.
- Mild steel fixings through a stainless panel.
Mixing grades on one job
There is nothing wrong with specifying both. On a coastal venue in Newcastle, Byron or the northern beaches we will regularly run 316 on the exposed alfresco servery, the drains and anything in the pool plant room, and 304 through the back-of-house kitchen where the surfaces are washed down every night. The materials schedule we hand over records which is which, so a maintenance contractor in five years does not apply pool-room cleaning chemicals to a 304 bench.
If the grade is the most interesting decision on your drawing, the drawing is not finished. Detailing beats specification almost every time.
What to send us
You do not need to nominate a grade to get a quote. Tell us the suburb, Sydney, Melbourne, Brisbane or elsewhere in Australia, whether the space is enclosed, what will be used to clean it and whether anything is submerged or permanently wet. We will nominate the grade, note it on the shop drawings, and tell you plainly if we think you have been sold an upgrade you do not need.