Coating Thickness Gauges
All you need to know
This guide explores the different types of coating thickness gauges, how they work, and key factors to consider when selecting the right gauge for your application.
Why Measure Coating Thickness?
The thickness of a coating affects its durability, protective properties, and overall performance. If a coating is too thin, it may not provide adequate protection against corrosion, wear, or environmental exposure. On the other hand, an excessively thick coating can lead to unnecessary material waste, increased costs, and potential adhesion problems.
Industries rely on coating thickness measurements to:
•Ensure compliance with industry standards (e.g., ASTM, ISO, SSPC, and NACE)
•Improve product quality and consistency
•Reduce material waste and costs
•Prevent failures due to incorrect coating applications
Gauge Types
There are two primary categories of coating thickness gauges: destructive and non-destructive.
1. Destructive Coating Thickness Gauges
Destructive gauges involve cutting through the coating to measure its thickness directly. These are often used when non-destructive testing is not feasible, such as when verifying multilayer coatings or when testing needs to be performed post-application.
•Cross-section Microscopes – These involve cutting a small sample of the coated surface and using a microscope to measure thickness.
•Paint Inspection Gauges (PIGs) – These tools use a blade to scrape away a section of the coating, revealing the thickness of each layer.
While destructive methods provide highly accurate results, they damage the tested surface, making them less ideal for finished products.
2. Non-Destructive Coating Thickness Gauges
Non-destructive gauges allow for repeated testing without damaging the coating or substrate. These are the most commonly used tools in industrial applications.
a. Magnetic Induction Gauges
Used for ferrous (magnetic) substrates like steel, magnetic induction gauges measure coating thickness based on how a magnetic field changes when passing through the coating.
•Ideal for measuring non-magnetic coatings (e.g., paint, zinc, plastic) on steel
•Highly accurate and widely used in automotive, shipbuilding, and construction industries
b. Eddy Current Gauges
Eddy current gauges are used on non-ferrous (non-magnetic) substrates like aluminum, brass, or copper. They work by generating an alternating electromagnetic field and measuring the disturbance caused by the coating.
•Commonly used for anodized coatings on aluminum
•Effective for thin coatings, such as powder coatings in aerospace applications
c. Ultrasonic Coating Thickness Gauges
Ultrasonic gauges use sound waves to measure coating thickness, making them ideal for non-metallic surfaces like plastic, wood, and composites. They can also measure multiple layers of coatings without damaging the material.
•Used in industries where non-metallic coatings are applied, such as automotive refinishing and aerospace
•Suitable for soft or delicate materials that cannot be subjected to magnetic or eddy current testing
d. Combination Gauges
Many modern coating thickness gauges combine magnetic induction and eddy current methods to measure coatings on both ferrous and non-ferrous substrates. These versatile tools are widely used in general industrial applications and automotive refinishing. The PosiTest DFT combo is a perfect example.
Factors to Consider
When selecting a coating thickness measuring gauge, consider the following:
1. Substrate Material
•Use magnetic induction for steel
•Use eddy current for aluminum and other non-ferrous metals
•Use ultrasonic gauges for plastic, wood, or composites
2. Coating Type
•Thin coatings may require high-precision instruments
•Multi-layer coatings may need ultrasonic gauges for accurate measurement
3. Accuracy and Calibration
•Ensure the gauge has proper calibration options
•Look for models that provide consistent, repeatable measurements
4. Portability and Ease of Use
•Handheld models are useful for field applications
•Digital displays and data logging can enhance efficiency
5. Industry Standards Compliance
•Make sure the gauge meets ASTM, ISO, or other applicable standards