Meaning and Purpose
4.1 Water causes the coating to degrade, so understanding how the coating is waterproof helps to predict its service life. A water mist test failure can be caused by a variety of factors, including defects in the coating itself, contamination of the substrate, or inadequate surface treatment. Therefore, the test can be used to evaluate individual coatings or complete coating systems.

4.2 Water mist testing is used for coating and substrate treatment research and development, specification acceptance and quality control in manufacturing. These tests typically lead to a determination of pass or failure, but can also measure the extent of failure. If there is no evidence of water-related failure after a specified time period, the coating system is considered to have passed.

4.3 Until the quantitative relevance of the coating or coating system is determined, the results obtained using water spray tests in accordance with this protocol should not be expressed as equivalent to a period of exposure to water in the natural environment.

4.4 The test setup is similar to the setup used in Practice B117, and it is feasible to convert the setup from salt spray testing to water spray testing. When converting from salt spray to water spray testing, care should be taken to remove all traces of salt from the cabinet and liquid storage tank.

ASTM D 1735-2021 “Determination of Water Resistance of Coatings by Water Mist Meter”

Scope of
1.1 This practice covers the fundamentals and operating procedures for testing the water resistance of coatings in equipment similar to salt spray testing.

1.2 This practice is limited to methods of obtaining, measuring and controlling conditions and procedures for water mist testing. It does not specify sample preparation, specific test conditions, or evaluation of results.

Note 1: Alternative practices for testing paint for water resistance include D870, D2247 and D4585.

1.3 Values expressed in SI units shall be regarded as standards. The values given in parentheses are for reference only.

ASTM D 1735-2021 “Determination of Water Resistance of Coatings by Water Mist Meter”

1.4 This standard is not intended to address all safety issues, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health and environmental practices and to determine the applicability of regulatory restrictions prior to use.

1.5 This international Standard has been developed in accordance with the internationally recognized standardization principles established in the Decision on Principles for the Development of International Standards, Guidelines and Recommendations issued by the Committee on Technical Barriers to Trade of the World Trade Organization.