A destructive dry Film Thickness Gauge is a measurement tool used to determine dry film thickness by cutting and removing cross-sections, making accurate V-grooves or geometric cuts in the coating, and measuring with a scale microscope. The actual thickness of a cross-sectional sample can also be measured with a micrometer.
Some destructive dry Film Thickness Gauges have special V-groove cutting tools and illuminated magnifiers to improve the accuracy of preparing samples for destructive measurements.
With dry film thickness gages, destructive repair of damaged sample areas is required, but the method is considered suitable for the following situations:
Non-destructive thickness measurement methods are not available or cannot be used.
Coatings go over wood, plastic, concrete, or other non-magnetic substrates that most non-destructive dry Film Thickness Gauges cannot. The destructive thickness measurement method is suitable for coatings on almost any substrate.
Measure individual coating thicknesses in multilayer coatings.
Verify or validate the results of non-destructive dry Film Thickness Gauges.
The following documents describe commonly used destructive measurement methods:
ASTM D4138, Standard Practice for Measuring Dry Film Thickness of Protective Coating Systems by the Destructive Cross-Section Method.
ASTM D1005, Standard Test Method for Dry Film Thickness of Organic Coatings Using Micrometers, Procedure D.
Destructive measurement methods are usually only used as a last resort. Human error in sample preparation and measurement reading can reduce its accuracy.
