ASTM G85 Testing: Complete Guide to Modified Salt Spray (Fog) Corrosion Testing for Coatings and Materials

Written by Rahul Verma | Updated: December 2, 2025

What is ASTM G85 Testing?

ASTM G85 describes standardized test processes for modified salt spray (fog) exposure, assessing the resistance of metals, coatings, and surface treatments to corrosion. Building on a basic ASTM B117 salt spray test, it introduces controlled variations in exposure conditions, such as cyclic wet/dry cycles, acidic solutions, or the addition of pollutants like SO₂, to more accurately simulate real-world corrosive environments.

The aim of testing according to ASTM G85 is to accelerate corrosion under controlled conditions, thereby helping to predict how materials or coatings will perform in harsh service conditions, such as marine atmospheres, industrial zones, or transportation environments.

In simple terms, this test determines a material or coating’s ability to resist corrosion under specific, modified salt spray conditions.

Why is ASTM G85 Testing Important?

Corrosion is a critical concern in industries where materials are constantly exposed to saltwater, humidity, and pollutants. ASTM G85 testing is vital because it helps:

Assess product durability and corrosion resistance in aggressive environments.
Ensure compliance with international quality and performance standards.
Support material and coating selection for outdoor, marine, and industrial applications.
Verify protective treatments, such as galvanizing, painting, or plating.

This method is frequently referenced in automotive, aerospace, and marine industry standards, as well as by OEMs and regulatory bodies to confirm that components meet corrosion performance requirements before being approved for field use.

Which Materials Can Be Tested Under ASTM G85?

ASTM G85 is suitable for evaluating a wide range of materials and coatings, including:

Metals: Steel, aluminum, copper, zinc, nickel, and their alloys.
Coatings: Paints, conversion coatings, metallic platings, and galvanic layers.
Composites and polymers (when coated or used in corrosive environments).

Typical test specimens include sheets, panels, fasteners, rods, or assembled parts—prepared according to the relevant product standard or specification.

What Information Do ASTM G85 Test Results Provide?

The test provides qualitative and quantitative information about corrosion behavior.

Parameter	Unit / Type	Description
Time to First Corrosion	Hours	Indicates coating breakdown or onset of rust.
Degree of Corrosion	% or visual rating	Extent of surface degradation or rusting.
Coating Adhesion	Pass/Fail	Resistance of coating to delamination after exposure.
Appearance Changes	Visual	Blistering, discoloration, pitting, or cracking.

These results help engineers compare material or coating performance, validate corrosion protection systems, and predict field life expectancy.

What Industries Use ASTM G85 Testing?

ASTM G85 is widely used in industries where components face challenging environments, including:

Automotive: Body panels, fasteners, chassis parts, and coatings.
Aerospace: Aluminum alloys, surface treatments, and protective coatings.
Marine: Offshore structures, ship components, and marine hardware.
Construction: Architectural metals, galvanized structures, and hardware.
Electronics and Consumer Goods: Corrosion protection of enclosures and hardware.

What Equipment Is Used for ASTM G85 Testing?

The primary equipment used includes:

Modified Salt Spray Chamber: Capable of maintaining controlled temperature, humidity, and spray cycles.
Solution Reservoirs: For preparing and delivering modified test solutions.
Nozzles and Air Atomizers: To create a consistent salt fog or cyclic spray.
Control Systems: For adjusting pH, temperature, and spray duration.
Accessories: Specimen racks, collection funnels, and temperature/humidity sensors.

How Is the ASTM G85 Test Performed?

Step-by-Step Procedure:

Specimen Preparation:
Test specimens are cleaned and coated or finished as per the intended end-use. Edges are sealed if required to prevent premature corrosion.
Test Solution Preparation:
A specific modified salt solution is prepared according to the chosen annex (e.g., acetic acid, SO₂, cyclic wet/dry).
Chamber Setup:
The test chamber is maintained at the required temperature and humidity.
Exposure:
Specimens are placed in the chamber at an angle (typically 15–30°) and exposed to continuous or cyclic fog according to the selected procedure.
Cycle Control:
Exposure may alternate between salt fog, drying, and humidity phases to simulate real-life environmental conditions.
Evaluation:
At defined intervals, specimens are inspected for signs of corrosion such as rusting, blistering, or coating breakdown.

What Are the Standard Test Conditions?

ASTM G85 includes five major annexes (A1–A5), each specifying different test conditions:

Annex	Test Type	Solution / Environment	Typical Use
A1	Acetic Acid Salt Spray (ASS)	NaCl + Acetic Acid	Decorative coatings
A2	Cyclic Acidified Salt Fog (CASS)	NaCl + CuCl₂ + Acetic Acid	Electroplated or anodized coatings
A3	Seawater Acidified Test (SWAT)	Synthetic seawater + Acid	Marine applications
A4	SO₂ Salt Spray (Prohesion Test)	NaCl + (NH₄)₂SO₄ + SO₂ gas	Industrial atmospheres
A5	Dilute Electrolyte Cyclic Fog/Dry Test	NaCl + Dry cycles	General corrosion resistance

Key Properties Measured

ASTM G85 evaluates the following key properties:

Corrosion resistance and coating durability under accelerated exposure.
Adhesion and integrity of coatings or platings after exposure.
Resistance to rust, pitting, or blistering.
Visual and structural degradation of materials under simulated environments.

Related Testing Methods

ASTM B117: Standard Salt Spray (Fog) Test – the base method for G85 modifications.
ASTM D1654: Evaluation of painted or coated specimens for corrosion resistance.
ASTM D714: Degree of blistering in paint coatings.
ISO 9227: Corrosion tests in artificial atmospheres – salt spray tests.
ASTM G44: Alternating immersion test for metals.

Conclusion

The ASTM G85 Modified Salt Spray Test provides a more realistic assessment of corrosion resistance than traditional salt fog tests by incorporating environmental variations such as acid and SO₂, and cyclic exposure.

By duplicating service conditions, ASTM G85 aids the manufacturer in the validation of protective coatings and metallic materials’ performance, durability, and reliability. This practice is considered indispensable in ensuring compliance, improving product design, and determining material lifespan in aggressive environments.

From automotive to aerospace applications, ASTM G85 remains a trusted standard for verifying corrosion performance and ensuring long-term product quality.

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FAQs on ASTM G85 Modified Salt Spray Test

What is the purpose of ASTM G85 testing?

ASTM G85 testing is performed to evaluate the corrosion resistance of metals, coatings, and surface treatments under modified salt spray conditions. It simulates more realistic environmental exposure—such as acid rain, industrial pollution, or marine environments—compared to the standard salt spray test (ASTM B117).

How does ASTM G85 differ from ASTM B117?

While ASTM B117 employs a continuous neutral salt fog environment, ASTM G85 introduces modifications such as acidic solutions, SO₂ exposure, or cyclic wet/dry conditions. These variations make ASTM G85 more representative of actual service conditions, thereby providing a more accurate prediction of real-world corrosion behavior.

How long does an ASTM G85 test take?

The duration varies depending on the annex used and product specification requirements. Typical tests range from 24 hours to over 1000 hours, with periodic inspections for corrosion initiation, coating failure, or surface changes.