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Choosing 304 or 316 stainless for sign letters
The choice is set by chlorides in the air, not by budget, and getting it wrong shows as rust streaks within a year.
304 is the standard austenitic stainless and the right answer for interiors and sheltered exteriors. It resists ordinary atmospheric corrosion indefinitely and costs less to buy and to polish.
316 contains molybdenum, which resists chloride attack. Chlorides are present near the sea, around swimming pools, on roads that are salted in winter, and in some industrial atmospheres. In those environments 304 develops pitting and then rust streaking down the face of the letter, usually within the first year and always on the most visible installation the client has.
The failure is cosmetic rather than structural, which is exactly why it matters: a sign exists to look right. Replacing rust-streaked letters on a seafront hotel costs far more than the grade difference would have, and the conversation happens in front of the client.
Where a project is marginal, specify 316. It is the cheaper mistake.
Specifications
| 304 | Interior and sheltered exterior |
|---|---|
| 316 | Coastal, pool areas, salted roads, industrial atmospheres |
| Failure mode of 304 in chlorides | Pitting then rust streaking, usually within a year |
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