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Coating thickness and thickness measurement

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COATING THICKNESS AND THICKNESS MEASUREMENT

Coating thickness represents the central quality characteristic of a coating film. It influences all functional characteristics of the coating film, especially its corrosion resistance . For this reason, fulfilling a required coating thickness is essential for overall coating quality.

When determining the coating thickness of a dry coating film, the appropriate measuring procedure is primarily dependent on the material combination of the coating system and substrate. In the case of dry film thickness, a distinction is made between destructive and non-​destructive measurement methods. Non-​destructive methods include, for example, the beta backscatter method, x-ray fluorescence analysis and the eddy current method (amplitude intensive or phase intensive).  Measurement of coating thickness is specified in standards such as ISO 2808, ASTM B487, ASTM B499, and ASTM B568.  The appropriate time to measure coating thickness is immediately after application.  Increased inspection reduces large scale rejections if defects are detected.

Duration of salt spray test (without red rust)

Reference thickness of the coating system*

240 Hours4 µm
480 Hours5 µm
600 Hours6 µm
720 Hours8 µm
960 Hours10 µm

*The reference layer thickness includes both base- and topcoat – depending on the composition of the coating system.

Relation of layer thickness to salt spray resistance as per DIN EN ISO 10683