If you’ve shopped for powder coatings, you’ve probably seen a spec sheet claim something like “1000 hours of salt spray resistance,” or encountered a number that’s several times higher. It sounds impressive, but what does that number actually tell you? And more importantly, how do you know if it’s a meaningful claim at all?
What ASTM B117 Actually Tests
ASTM B117 is the standard test method for continuous salt spray (fog) testing. A coated panel goes into a sealed chamber where it’s exposed to a fine, continuous mist of 5% salt water at a steady 95°F (35°C). Panels are typically scribed, meaning a deliberate scratch is cut down to bare metal before testing begins.
At set intervals, technicians pull the panel and measure:
- Scribe creep: how far corrosion has crept out from that scratch line
- Blistering: bubbling or lifting of the coating film
- Rust or corrosion on the surface itself
A meaningful result reports all of it together: the test duration, the pass/fail criteria, the substrate, and the pretreatment. A number by itself is close to meaningless.
Our Standard: 1000 Hours, Fully Specified
Our standard coatings are rated at 1000 hours of B117 exposure, with a maximum of 1/8″ scribe creep, no rusting, and no blistering. Testing is performed on cold rolled steel panels pretreated with Bonderite 1000 and sealed with Parcolene 60. That’s a real, industry-standard benchmark, and it’s one that essentially any quality powder coating on properly pretreated steel should be able to meet.
Why Some “Bigger” Numbers Don’t Mean What They Imply
We’ve seen competitive marketing materials advertising 5000, 6000, even 12 000 hours of salt spray resistance. On paper, that looks dramatically better than a 1000-hour rating. In practice, these claims are almost always missing the details that would let you evaluate them:
- No substrate specified. Corrosion resistance depends heavily on what’s under the coating. A number with no substrate or preparation listed can’t be compared to anything.
- No pass/fail criteria. “12 000 hours” of what, exactly? Zero creep? Some visible rust but no blistering? Without a defined standard, the number is just a duration, not a result.
- No mention of scribing. An unscribed panel has no path for corrosion to travel along a defect, so it will naturally outlast a scribed one by a wide margin. Comparing an unscribed result to a scribed one isn’t apples to apples, it’s not even the same test.
When any of that information is missing, the number isn’t really a test result. It’s a marketing figure. At best, it reflects a best-case scenario dressed up to look like a standard rating. At worst, it’s a claim with no real testing behind it at all, designed to win a spec comparison rather than to describe actual performance.
How to Read a Salt Spray Claim
Before comparing any two coatings on salt spray performance, ask for:
- The substrate and pretreatment used
- Whether the panel was scribed
- The pass/fail criteria at the stated hour mark (creep distance, rusting, blistering)
If a manufacturer can’t or won’t answer those three questions, treat the number with real skepticism. A well-documented 1000-hour rating with clear criteria tells you far more than an undocumented 12 000-hour claim.
The takeaway: salt spray hours are only useful when they come with the full picture: substrate, pretreatment, scribe condition, and defined pass/fail limits. Anything less is just a number, not a spec.
Have questions about how our testing standards compare to a claim you’ve seen elsewhere? Contact our team, either through your technical sales representative, or through our office. We’re happy to walk through the data with you.