Historical
ISO 2808:1997
Paints and varnishes - Determination of film thickness
This International Standard reviews and specifies a number of methods that are applicable to the measurement of the thickness of organic coatings applied to a substrate. It does not apply to metallic coatings. Some of the techniques described can be adapted for the measurement of the thickness of detached coatings. The principles of the methods, their particular field of application and the expected precision are given in table 1.
This International Standard also defines terms concerning the determination of film thickness.
| Methods of film thickness measurement | ||||
|---|---|---|---|---|
| Number and description | Techniques and applications | Typical instrument bias1) and precision | Remarks | |
| Method No. 1 | A Comb gauge | ---- | Measurements give an approximate indication of the thickness of the wet film. | |
| Assessment of wet-film thickness | B Wheel gauge | Bias: ± 2,5 % + 1 μm | May be used in laboratories and on site. | |
| C By weighing For measurement of wet-film thickness of freshly painted surfaces. | Reproducibility: ± 15 μm | Method 1C may also be used for determining the dry-film thickness, but in the laboratory surfaces only. | ||
| Method No. 2 | For use on films too soft to be measured by methods which use a presser foot or probe. | Determinations are not precise | Provides a check that the mean thickness lies between specified limits. The film remains undamaged. | |
| Determination of dry-film thickness by calculation from the ratio of dry-film mass to dry-film area | ||||
| Method No. 3 | ||||
| Measurement of dry-film thickness by mechanically contacting instruments | A Micrometer method. For use on test panels or painted surfaces that are substantially plane. | Bias: ± 2 μm Reproducibility: ± 30 % for low and 20 % for higher film thicknesses | The film has to be hard enough to resist indentation on closing the micrometer jaws. The film is damaged in the test. The film thickness shall be greater than 25 μm unless the film is detached. | |
| B Dial gauge method Test panels or painted surfaces that are substantially plane or have a curvature in one direction | Reproducibility: ± 10 %, with a lower limit of 2 μm | The film has to be hard enough to resist indentation on lowering the gauge or electric-device presser foot. | ||
| Method No. 4 | ||||
| Measurement of dry-film thickness by the profilometric method | Recommended as a referee method for painted surfaces that are substantially plane. | Reproducibility: ± 10 %, with a lower limit of 2 μm | The film has to be hard enough to resist indentation by the profile-tracing stylus. The film is damaged in the test. | |
| Method No. 5 | ||||
| A Microscopic examination of cross-section. | Bias: 2 μm | A portion of the painted article is cut out and mounted in resin. | ||
| Measurement of dry-film thickness by microscope methods | Recommended as a referee method for films on substrates of varying profile, for example grit-blasted surfaces. | Reproducibility: ± 10 % | The film is damaged in the test. | |
| B Wedge cut method. Not applicable to brittle or friable films. | Reproducibility: ± 10 %, with a lower limit of 2 μm | A special cutting tool or paint borer is required to cut through the film. | ||
| Both A and B can be used for thicknesses of individual coats in a paint system | The film is damaged in the test. | |||
| C Surface profile measuring method. Applies to transparent films and to films which can be cleanly removed from the substrate. | Reproducibility: ± 10 % | A special microscope is used to examine the profile of the film (split-beam microscope). Only transparent films remain undamaged. | ||
| Method No. 6 | For magnetic metallic substrates | |||
| Magnetic methods | A Magnetic-induction principle | Bias: ± 2 % +1 μm Reproducibility: ± 10 % | The film has to be hard enough to withstand the pressure of the probe. | |
| B Permanent-magnet pull-off principle | Bias: ± 5 % +1 μm | May be used on site. | ||
| Method No. 7 | For non-magnetic metallic substrates | Bias: ± 2 % + 1 μm | Instruments operate on the eddy-current principle. | |
| Eddy current method | Reproducibility: ± 10 % | The film has to be hard enough to withstand the pressure of the probe. | ||
| May be used on site. 3 | ||||
| Method No. 8 | Used when contact by the measuring instrument with the coating needs to be avoided. | Instruments operate on the beta-particle back-scatter principle (method No. 8A) or the X-ray fluorescence principle(method No. 8B). | ||
| Non-contact methods | Applicable to painted surfaces which are substantially flat. | Reproducibility: ± 10 % | ||
| Paint films have to be homogeneous for measurements to be accurate. | ||||
| Method No. 9 | Applicable to films on substrates of varying profiles, for example grit-blasted steel panels, and to films on polymeric substrates if the substrate is not affected by the paint solvent. | The coating mass is determined by dissolving the coating without dissolving the substrate. The mass of coating divided by the density and the area of the coating gives the average coating thickness. | ||
| Gravimetric (dissolving) method | ||||
| Method No. 10 | For dry coatings on magnetic metallic substrates having a rough (blast-cleaned) surface. | Instruments operate on the magnetic-induction principle. | ||
| Determination of dry-film thickness on blast-cleaned steel substrates | May be used on site. In some cases, method No. 5A or method No. 9 may also be used. | |||
| 1) The bias data are based on information supplied by the instrument manufacturers | ||||
Content Provider
International Organization for Standardization [iso]
