Salt Spray Testing: How to Read the Hours

Few numbers in a powder coating data sheet are quoted as proudly as the salt spray hours – and few are as easy to misunderstand. Salt spray (neutral salt spray per ISO 9227 or ASTM B117) is a fast, standardized corrosion test, not a prophecy of outdoor life. Reading it correctly means knowing what it measures, where results are biased, and how to compare one supplier report to another.

What Salt Spray Actually Tests

The test exposes scribed and unscribed coated panels to a continuous fine mist of 5% sodium chloride solution at 35 degrees Celsius for a set number of hours. It measures how well the coating system – powder, pretreatment and substrate together – resists an aggressively corrosive environment at the scribe and at edges. It is a comparative screening tool, useful for judging formulations and processes against each other, not a predictor of real-world years.

What It Does Not Test

• UV and weathering: salt spray does not simulate sunlight, so it says nothing about chalking or fading
• Mechanical abuse: impacts, scratches and abrasion are separate tests
• Real environments: coastal salt, road salt and chemical atmospheres behave differently from a neutral salt fog
• Adhesion at the interface: creepage at the scribe is the closest proxy, but it is not an adhesion test

Scribes, Edges and Corners: Where Results Are Decided

A panel corrosion story is written at its weakest points. The scribe – a cut through the coating to the metal – tests how well the system stops corrosion creeping under the film from a damaged area. Edges and corners have thin coating and attract corrosion faster than flats. Two reports can both say 1000 hours while one panel shows 1 mm creepage and another shows 6 mm, depending on where and how the panel was prepared. Always ask for creepage numbers and photos, not just pass/fail hours.

How to Read the Results

• Creepage at the scribe: measure the maximum and average distance corrosion travels under the film (often specified as max 2 mm after the test)
• Blistering: rate per ISO 4628-2 by size and density – small, few blisters beat large, many
• Rust on unscribed areas: any rust on a clean surface is a coating failure, not a creepage issue
• Edge corrosion: report how far corrosion advances from edges and corners separately

Why 1000 Hours in One Lab Differs From 1000 Hours in Another

Salt spray results depend on details the headline hides: panel preparation (blast profile, conversion coating), scribe geometry, panel position in the chamber, fog uniformity, and how ratings are assigned. A reputable report states the standard, the panel system, the scribe method and the evaluation criteria. If a supplier quotes hours without any of that context, treat the number as marketing.

How to Use Salt Spray in Your Procurement

• Specify the test standard, duration, scribe type and the pass criteria (for example max 2 mm creepage)
• Compare suppliers using the same standard and same panel preparation
• Ask for photos of the tested panels, not just a certificate
• Use salt spray together with QUV and mechanical tests for a balanced view of the coating

Get a Salt Spray Report You Can Trust

We test our formulations to ISO 9227 with defined panel preparation and evaluation, and we share the standard, the scribe method and photos with the report. Tell us your target hours and pass criteria, and we will confirm the formulation and film build that achieve them – and prove it on your specified panel system.