What Does Dry Film Thickness Gauge, Destructive Mean?
Dry film thickness gauge, destructive is a measuring tool used to determine dry film thickness by cutting and removing a cross section, making a precise v-groove or geometric cut on the coating and then measuring it with a scaled microscope. The actual thickness of the cross section sample can also be measured by a micrometer.
Some destructive dry film thickness gauges feature a special v-groove cutting tool and illuminated magnifier to improve the accuracy of preparing the destructive measurement sample.
Corrosionpedia Explains Dry Film Thickness Gauge, Destructive
Using a dry film thickness gauge, destructive requires repairs to the damaged sample areas but the method is considered appropriate in the following instances:
- Non-destructive methods for thickness measurement are not possible or electronic gauges are not available or cannot be used.
- The coating is over wood, plastic, concrete or other non-magnetic substrates where most non-destructive dry film thickness gauges can’t be used. The destructive thickness measurement method is applicable for coatings over almost all substrates.
- To measure individual coating thickness in a multi-layer coating.
- To verify or validate the result from a non-destructive dry film thickness gauge.
Commonly used destructive measurement methods are described in the following documents:
- ASTM D4138, Standard Practices for Measurement of Dry-Film Thickness of Protective Coating Systems by Destructive Cross-Section Means.
- ASTM D1005, Standard Test Method for Measurement of Dry-Film Thickness of Organic Coatings Using Micrometers, Procedure D.
The destructive measurement method is generally used only as a last resort. Its accuracy is reduced by human errors in sample preparation and measurement reading.