Salt spray testing is an accelerated corrosion test used to evaluate how coatings, plated parts, and treated surfaces resist degradation in salt-laden environments. It exposes samples to a continuous fine mist of salt solution inside a controlled chamber, compressing months of corrosive exposure into days or weeks. This test is commonly used in the automotive, appliance, construction, and general manufacturing industries to compare finishes, validate processes, and meet material specifications.

What Is Salt Spray Testing?

Salt spray testing places coated or plated samples inside a sealed chamber where a 5% sodium chloride solution is atomized into a fine fog at a controlled temperature, typically 35°C (95°F). The salt fog settles continuously on the samples, creating a highly corrosive environment that accelerates the same types of degradation that occur over time in outdoor and industrial service conditions.

After a defined exposure period, samples are removed, rinsed, and evaluated for corrosion-related changes: rusting, blistering, underfilm creep from a scribed line, coating breakdown, and loss of adhesion. The severity of these changes is rated against standardized scales or specification-defined acceptance criteria.

The results are used in product development, production quality control, supplier qualification, and failure analysis. Salt spray data provides a consistent, repeatable basis for comparing coating systems, verifying pretreatment processes, and confirming that materials meet the corrosion resistance requirements in OEM and industry specifications.

What to Expect From Salt Spray Testing

Salt spray testing is commonly used when you need a fast, repeatable way to compare corrosion resistance or validate coating and pretreatment performance against a known benchmark.

Benefits

• Accelerated Feedback - Produces corrosion data in days or weeks rather than the months or years required for natural outdoor exposure.
• Repeatable Conditions - Maintains consistent temperature, fog density, and solution concentration so results can be compared across samples tested at different times.
• Quality Control Utility - Helps flag shifts in performance that may point to issues with pretreatment chemistry, curing parameters, film build, or surface preparation before defective product ships.
• Cost-Effective - Typically less expensive than extended cyclic corrosion programs or multi-year outdoor exposure testing.
• Widely Specified - Commonly referenced across automotive, military, industrial, and architectural coating specifications, which simplifies how requirements and results are communicated.

What You Should Know

Salt spray hours do not translate cleanly into real-world service life, and the constant salt fog environment can miss important field conditions like UV exposure, temperature cycling, and dry-wet transitions. Results can also be sensitive to sample preparation details like masking, scribe consistency, and surface cleanliness, so it’s often best used as a screening or comparison tool, with additional testing selected based on the actual end-use environment.

Uses and Applications

Salt spray testing is used wherever corrosion resistance affects product safety, appearance, warranty, or service life. Common applications include:

•                    Automotive and Transportation: Evaluating e-coat, primer/topcoat systems, plated fasteners, and underbody components against OEM corrosion specifications.

•                    Appliances and Consumer Goods: Validating painted metal housings, brackets, and hardware that will be exposed to humidity and cleaning agents.

•                    Construction and Architectural Products: Testing coated metals, fasteners, and structural components for coastal or industrial environments.

•                    Industrial Equipment and Agriculture: Evaluating coatings and treatments on parts exposed to chemicals, outdoor weathering, and washdown.

•                    General Manufacturing: Process verification for pretreatment changes, paint line adjustments, or new supplier qualification.

How Is the Salt Spray Test Conducted?

The procedure follows a defined sequence, though specific details vary by standard and customer specification:

1.                  The test plan is defined, including the applicable standard, exposure duration, acceptance criteria, sample count, scribe requirements, and inspection intervals.

2.                  Samples are labeled, photographed, and documented (film build, substrate type, coating system). If scribes are required, they are applied to a consistent depth and width using a carbide-tipped tool.

3.                  The chamber is stabilized to the required operating conditions (35°C, 5% NaCl solution at pH 6.5 to 7.2 for neutral salt spray per ASTM B117) before samples are loaded.

4.                  Samples are positioned at 15° to 30° from vertical, spaced to avoid drip paths and shielding between panels, and exposed to continuous salt fog for the specified duration.

5.                  After exposure, samples are rinsed with clean water to remove salt deposits, allowed to dry, and evaluated against the defined acceptance criteria.

Evaluation typically includes visual inspection with photo documentation, corrosion creep measurement at scribed lines per ASTM D1654, rust area ratings per ASTM D610, and blister ratings per ASTM D714.

Blister Size Ratings (ASTM D714)

Blister frequency is reported alongside the size rating as Dense (D), Medium Dense (MD), Medium (M), or Few (F). For example, a rating of 6MD indicates medium-sized blisters at medium dense frequency.

Rust Grade Ratings (ASTM D610)

What Kind of Equipment Is Used to Perform This Test?

Salt spray testing is performed in a dedicated corrosion chamber designed to generate and maintain a consistent salt fog environment. The chamber atomizes a 5% sodium chloride solution through a nozzle system, dispersing it as a fine fog that settles on the test samples at a controlled collection rate, typically 1.0 to 2.0 mL per hour over an 80 cm² collection area per ASTM B117.

Chamber temperature is maintained at 35°C ± 2°C, and the solution pH is held between 6.5 and 7.2 (as collected) to ensure consistent corrosive conditions. Internal baffles and sample positioning racks allow panels to be placed at the required angle without shielding or drip contamination between specimens.

At ACT Test Panels, we use salt spray chambers that are regularly calibrated and monitored to maintain the operating parameters required by ASTM B117 and other applicable standards. Chamber conditions are documented throughout the test to ensure the data supports meaningful, specification-aligned results.

Test Methods

Test methods include:

•             Neutral Salt Spray (NSS)

•             ASTM B117

•             Ford BI 103-01

•             GM 4298P (Superseded 12/01/10)

•             GMW3286

•             ISO 9227

•             JIS Z2371

•             Copper Accelerated Salt Spray (CASS)

•             ASTM B368

•             GMW14458

•             Acetic Acid Salt Spray

•             ASTM G85 (Annex A1 and A2)

The Role of Test Panels in Salt Spray Testing

Variability in the test substrate can affect salt spray results. Differences in the metal alloy, surface finish, cleaning process, or pretreatment chemistry between panels can produce different corrosion outcomes even when the coating is identical. A panel with inconsistent zinc phosphate crystal coverage, for example, may show premature blistering that reflects the panel preparation rather than the coating’s actual corrosion resistance.

At ACT Test Panels, we manufacture panels from bare substrate through full paint systems, with each coating layer applied in compliance with the material manufacturer’s specification. This ensures that the salt spray test is measuring the performance of the coating technology, not the quality of the panel.

Salt spray testing is also commonly run as part of a broader environmental test program. An automotive coating qualification might include salt spray (ASTM B117), cyclic corrosion (SAE J2334 or GMW14872), humidity (ASTM D2247), and UV exposure (ASTM G154 or ASTM D4587), all conducted on panels from the same production lot to maintain consistent baselines across the full test matrix.

Contact ACT Test Panels for Your Salt Spray Testing Needs

ACT Test Panels has supported the global coatings industry since 1981 with reliable and reproducible test panels and objective third-party testing services. Salt spray testing is one of many environmental exposure tests performed in our ISO 17025 accredited laboratory, alongside cyclic corrosion, humidity, UV exposure, and more.

Contact us today to get a custom quote or explore our test panels.

Frequently Asked Questions

How Many Hours of Salt Spray Testing Equals One Year of Outdoor Exposure?

There is no reliable universal conversion. Real-world corrosion depends on climate, design geometry, drainage, coating damage, and maintenance cycles, none of which are replicated in a constant salt fog chamber. Salt spray results are best used for comparing finishes under controlled conditions, verifying process stability, and confirming that materials meet a defined specification.

How Long Does a Salt Spray Test Take?

Duration depends on the applicable standard and specification. Neutral salt spray tests per ASTM B117 commonly run from 24 to over 1,000 hours, depending on the coating system and the end-use requirements. Many programs include intermediate inspection points at defined hour intervals to track how degradation progresses over time.

How Much Does Salt Spray Testing Cost?

Pricing varies based on sample quantity, test duration, scribe requirements, inspection frequency, and reporting detail. Request a quote so that accurate pricing can be provided based on the exact scope of your program.

What Are the Sample Requirements for Salt Spray Testing?

Requirements depend on the applicable standard and acceptance criteria. Key considerations include clean, fully cured samples with clear identification and labeling, and sufficient surface area to evaluate corrosion consistently. If scribes or edge preparation are specified, those details should be defined before the test begins to ensure consistent and comparable results.