Salt Spray Testing for Outdoor Furniture: ISO 9227 Hours, Ratings and What to Ask Suppliers

Quick answer. ISO 9227 defines how a salt spray (salt fog) test is run — not what result counts as a pass. When a supplier quotes "480h salt spray", the meaningful questions are: which method (NSS, AASS or CASS), which substrate and coating system, which duration was specified, and what was evaluated at the end (for example, corrosion creep from a scribe line). Hour benchmarks like 240h / 480h / 720h are common reference points in outdoor furniture RFQs — they are practice, not grades defined by ISO 9227 itself.

What ISO 9227 actually tests

ISO 9227 — Corrosion tests in artificial atmospheres — Salt spray tests specifies three accelerated corrosion test methods: NSS (neutral salt spray), AASS (acetic acid salt spray) and CASS (copper-accelerated acetic acid salt spray). The standard fixes the chamber conditions — solution concentration, temperature, fog collection rate, specimen angle — so that results are comparable between laboratories. What it deliberately does not do is define acceptance criteria, quality grades, or service-life predictions. Those come from the buyer's specification, a product standard, or a coating classification system.

What the test measures — and what it doesn't

What it measures well: the relative corrosion resistance of a coating or material system under aggressive chloride exposure. It is genuinely useful for comparing finishes (for example, two powder-coating systems over the same galvanized steel) and for batch screening against a previously approved sample.

Which method applies: NSS (neutral salt spray) is the default for furniture coatings and the method most buyers mean when they say "salt spray". AASS and CASS are more aggressive variants used mainly for evaluating certain decorative finishes (for example on plated or anodized parts). If a supplier's report says "salt spray tested" without naming the method, that is the first thing to clarify — NSS 480h and CASS 480h are very different exposures.

What it doesn't do:

• It does not reproduce real weathering — there are no UV cycles, no wet/dry thermal cycling, no abrasion.
• It does not convert to outdoor years. A 500-hour result does not mean "500 days before rust". Correlation between salt spray hours and field life depends on the coating system, the substrate, and the installation environment.
• For painted and powder-coated steel, the informative part of the result is usually the evaluation after exposure — blistering and corrosion creep measured from a scribed cross — which follows coating-specific assessment practice. For selecting protective paint systems by environment, the ISO 12944 series defines corrosivity categories (C1 through C5, plus CX) used across the coatings industry.

In short: salt spray is a strong comparative screening tool and a weak life-prediction tool. Specify it for what it is.

Common hours benchmarks in outdoor furniture RFQs

The durations below are typical reference points seen in outdoor furniture procurement practice. They are not ISO 9227-defined grades — always define the duration and the acceptance criteria in your own specification.

Two caveats worth putting in writing:

1. More hours is not automatically better furniture. Coating thickness, pretreatment and substrate preparation frequently matter more to real-world durability than an extra few hundred hours of fog. A thick, well-pretreated coating at 480h can outperform a thin coating that survived 720h on a flat panel.
2. Ask what was tested. A flat test panel and a finished welded bench with joints, edges and cut ends are different corrosion scenarios. Welds and cut edges are where real failures start.

What to ask suppliers — checklist

Before you accept "passed salt spray testing" in a quote, ask eight things:

1. Which method — NSS, AASS or CASS? (NSS is the default for furniture; AASS/CASS are more aggressive and used for specific coating systems.)
2. Which duration was specified, and what duration was actually achieved?
3. Which substrate and coating system — galvanized steel? powder coat type and nominal thickness in microns?
4. What was evaluated at the end — corrosion creep from a scribe line, blistering rating, or appearance only?
5. Which laboratory issued the report, and can the report number be verified with that lab?
6. Was the test on the actual product or finish, or on a generic flat panel?
7. Is the report current for the finish system being quoted — or is it an old report for a different coating supplier?
8. Can acceptance criteria be written into the PO — duration, method, evaluation criteria — so the test is contracted, not just advertised?

The model sentence to require in specifications and factory profiles:

> "Tested to ISO 9227 (NSS) per factory test report No. ___; certification status varies by factory — see each factory profile."

And the honest baseline for any factory's documentation: test reports available on request per factory.

FAQ

Q1 — Is ASTM B117 the same thing?
Broadly equivalent for the neutral salt spray method — ASTM B117 is the standard US practice for operating a salt fog apparatus, and ISO 9227 NSS is its closest international counterpart. Many tenders accept either; check which one your tender cites and ask the supplier to match it.

Q2 — Does 720 hours mean the bench will last 720 days outdoors?
No. There is no fixed conversion from salt spray hours to outdoor service life. Field durability depends on the coating system, the installation environment, drainage and maintenance. Use the hours to compare systems, not to promise years.

Q3 — Can salt spray be combined with other tests?
Yes — and it should be. Salt spray covers corrosion only. Coating appearance and color retention under sunlight are evaluated by separate weathering tests, and structural safety by the mechanical standards for seating (see our EN 1728 vs EN 581 guide). A complete outdoor furniture specification touches all three.

Q4 — We are building in a desert climate — is salt spray still relevant?
Partly. In desert environments, high UV and thermal cycling dominate coating degradation, so weathering performance matters more. But salt spray still matters for coastal Gulf cities, for poolside installations, and for any buyer serving winter de-icing-salt climates. For how material choice interacts with climate, see our cast aluminum vs stainless steel comparison, and browse park & street bench constructions.

Q5 — How long and how costly is a salt spray test?
A 240–480h NSS run takes roughly the same number of calendar days in the chamber, plus preparation and evaluation — so test time is measured in weeks, not days, and rush jobs should be treated with suspicion. Cost varies by lab, duration and sample count; get a quote directly from the test laboratory. What matters more than the fee: the report must state the method, duration, specimens and evaluation criteria — a one-line "passed 480h" certificate answers none of the questions in the checklist above.

For how factory documentation is checked before listing, see the verified factory directory.

References

• ISO 9227 — Corrosion tests in artificial atmospheres — Salt spray tests (ISO; confirm the current edition in the ISO catalogue)
• ISO 12944 (series) — Paints and varnishes — Corrosion protection of steel structures by protective paint systems (corrosivity categories C1–C5 and CX)
• ASTM B117 — Standard Practice for Operating Salt Spray (Fog) Apparatus (ASTM International)