Glossary > #ISO 2808

ISO 2808 Standard

ISO 2808:2019 is an international standard from the International Organization for Standardization (ISO) that specifies methods for measuring the thickness of coatings applied to substrates. This standard is key to quality control in the paint and varnish industry, ensuring that coatings meet specific application requirements in terms of durability, appearance, and performance. The standard offers detailed procedures for measuring wet film thickness, dry film thickness, and thickness of uncured powder coating layers. Precise layer thickness measurement is essential because it affects the protective capabilities and aesthetic qualities of the coating.

Key Terms and Definitions

1. Layer Thickness

  • Definition: The vertical distance between the upper surface of the layer and the surface of the substrate. It is a critical parameter for coatings, affecting both protective and aesthetic qualities.

2. Wet Film Thickness

  • Definition: The thickness of freshly applied wet coating, measured immediately after application. Precise measurement ensures the correct amount of coating material is applied, achieving the required dry film thickness.

3. Dry Film Thickness

  • Definition: The thickness of the coating after drying and curing. This measurement is critical for assessing properties such as adhesion, coverage, and resistance.

4. Uncured Powder Coating Layer Thickness

  • Definition: The thickness of the powder coating before curing. Precise measurement ensures optimal application and performance after curing.

5. Relevant Surface Area

  • Definition: The area of an object that is coated or to be coated, affecting the usability and appearance of the coating.

6. Test Area

  • Definition: A designated part of the relevant surface area where a representative number of measurements are performed to ensure consistency and reliability.

7. Measurement Area

  • Definition: The area over which a single measurement is performed, important for local and precise readings.

8. Minimum and Maximum Local Layer Thickness

  • Definition: The range of layer thickness values found on the relevant surface area of the test sample, critical for quality control.

9. Average Layer Thickness

  • Definition: The arithmetic mean of all dry film thickness measurements in the test area or the result of gravimetric determination, providing an average value that represents the overall coating application.

Measurement Methods

ISO 2808:2019 categorizes methods for determining layer thickness into mechanical, gravimetric, optical, magnetic, radiological, photothermal, acoustic, and electromagnetic techniques. Each technique is adapted for specific coatings and substrates.

1. Mechanical Methods

  • Comb Gauge: A simple tool with teeth of various lengths used to measure wet film thickness.
  • Wheel Gauge: A rotating gauge that measures thickness by pointer displacement.
  • Dial Gauge: Measures thickness with a mechanical probe contacting the layer surface.

2. Gravimetric Method

  • Measures thickness by weighing coated and uncoated samples, using the mass difference along with known density and area.

3. Optical Methods

  • Cross-Sectioning: Involves cutting through the coating and measuring thickness under a microscope.
  • White Light Interferometry: Uses white light interference patterns to measure thickness with high precision.

4. Magnetic Methods

  • Magnetic Pull-Off Gauge: Suitable for non-magnetic coatings on magnetic substrates.
  • Eddy-Current Gauge: Used for non-conductive coatings on non-ferrous metal substrates.

5. Radiological Method

  • Beta Backscatter Method: Uses beta radiation to measure thickness, ideal for metal substrates.

6. Photothermal Method

  • Measures thickness based on thermal response to a modulated heat source.

7. Acoustic Method

  • Ultrasonic Reflection: Uses ultrasonic waves to determine thickness from the delay of reflected waves.

8. Electromagnetic Method

  • Terahertz Method: Uses terahertz radiation to penetrate coatings and measure thickness using reflected signals.

Applications and Accuracy

Each method detailed in ISO 2808:2019 has specific fields of application, accuracy levels, and limitations. The choice depends on the type of coating, substrate, required accuracy, and equipment availability. Precise layer thickness measurement is essential to ensure that coatings meet performance specifications and avoid premature failure.

Factors Affecting Accuracy

  • Surface Roughness: Can affect readings, particularly with magnetic and mechanical methods.
  • Substrate Material: Affects the choice and accuracy of the method.
  • Coating Composition: Additives such as fillers and pigments can affect measurement accuracy.

Measurement on Rough Surfaces

  • Special methods in Appendix B of ISO 2808:2019 ensure accurate readings despite surface irregularities.

Measurement on Wooden Substrates

  • Appendix C provides guidance for measuring layer thickness on wood, considering its porous nature and measurement challenges.

ISO 2808:2019 offers comprehensive methodologies for precise determination of coating thickness, which is essential for manufacturers and quality control professionals to ensure that coatings meet design specifications and perform effectively. Since coatings are essential for protection and aesthetics, precise layer thickness measurement is necessary to maintain quality in the paint and varnish industry.