📏 Paint coating thickness

Automotive PN-EN ISO 2808

Overview

STATUS (as of 02.11.2026). PN-EN ISO 2808:2020-01 — Polish version (published 31.05.2022), implements EN ISO 2808:2019 and ISO 2808:2019 [IDT]; it replaced PN-EN ISO 2808:2008 (Polish version). The catalogue card carries no withdrawal notice — the standard is current. ISO 2808:2019 (fifth edition, 26.07.2019) replaced the 2007 edition; in the ISO catalogue the standard has the status “confirmed” (stage 90.93). Changes in the 2019 edition: terms according to ISO 4618 and ISO/IEC Guide 99, a revised principle, white-light interferometry added (method 6C) and the terahertz method added (method 11), methods adapted to the current state of metrology, a revised overview of the methods and their precision in Annex A, measurement on rough surfaces moved to Annex B, a new Annex C on measurements on wood.

SCOPE (Clause 1). The standard describes methods for measuring the thickness of coatings applied to a substrate — wet-film thickness, dry-film thickness and the thickness of uncured powder coating layers — and gives for each method its field of application, existing specific standards and precision. The coats of a multi-layer system are numbered from the substrate (coating 1 is the first one applied); some other standards count in the reverse order.

METHODS (table of contents of the standard). Wet film: comb gauge (1A), wheel gauge (1B), dial gauge (1C), difference in mass (2), photothermal method (3). Dry film: difference in thickness (4A), depth gauging (4B), surface profile scanning (4C), difference in mass (5), cross-sectioning (6A), wedge cut (6B), white-light interferometry (6C), magnetic pull-off (7A), magnetic flux (7B.1), magnetic induction (7B.2), eddy current (7C), beta backscatter (8), photothermal method (9), ultrasonic reflection (10), terahertz method (11). Uncured powder coating layer: difference in mass (12), magnetic induction (13A), eddy current (13B), photothermal method (14).

WET FILM (Clause 4.2). In the mechanical methods the instrument passes through the layer to the substrate, and the difference between the points of contact with the substrate and with the coating surface is the wet-film thickness read off; the substrate at the measuring point must be flat in at least one direction (curvature in one plane, e.g. pipes, is permissible). All mechanical methods contain a systematic error — they show a thickness smaller than the actual one by at least the mean diameter of the pigment particles — and the wheel gauge (1B) must be wetted by the coating material, otherwise the reading can be exaggerated.

MAGNETIC AND EDDY-CURRENT METHODS (ISO 2178, ISO 2360). The magnetic methods use the fact that the magnetic flux density close to a field source depends on the distance to a magnetizable substrate — they serve to measure non-magnetizable coatings on magnetizable substrates, e.g. paint on steel; in the inductive method the relationship between voltage and thickness is nonlinear and is determined by calibration. The amplitude-sensitive eddy-current method serves for non-conductive coatings on non-magnetic conductive metals, e.g. paint on aluminium, in particular for oxide layers produced by anodizing: the high-frequency field of the probe induces eddy currents in the substrate whose density depends on the distance between the coil and the metal. The sensitivity of the probe decreases as the coating thickness increases. Before use the instrument is calibrated or adjusted with thickness reference standards (coatings on base metal or foils) on base metal whose material, geometry and surface are similar to those of the test item, and the calibration is checked at the place of inspection when the instrument is put into operation, after a change of material or geometry of the item and after a change of conditions. The result is the arithmetic mean of several single measurements in a defined area, with the standard deviation; unless otherwise agreed, at least five measurements are recommended (ISO 2360, 7.2). The result is affected by, among other things, the thickness and properties of the substrate, the proximity of an edge, curvature, roughness, probe pressure and tilt, and temperature.

WHAT WE DO NOT GIVE HERE. The description of the individual ISO 2808 methods for dry films (Clause 5) and their precision from Annex A — the available text of the standard ends at the gravimetric method for wet films (4.3.4); we describe the magnetic and eddy-current methods according to ISO 2178 (FDIS text of 2015) and ISO 2360:2017. The measuring ranges, accuracy and resolution of instruments — they depend on the instrument and probe; the minimum distance from an edge — it depends on the probe system and is determined experimentally (ISO 2360, 5.4). We do not give the thicknesses of individual paint coats — they are set by the product specification.

Method principle

The method is chosen according to the kind of layer (wet, dry, powder coating before curing) and to the coating–substrate combination. The mechanical and optical methods measure the thickness directly — from a difference in height, on a cross-section or on a wedge cut — and the gravimetric ones from a difference in mass. In the magnetic methods the probe responds to the change of magnetic flux with the distance to a magnetizable substrate, and in the eddy-current method to the change of coil impedance caused by the currents induced in a conductive substrate; after calibration with thickness reference standards the instrument converts the signal into coating thickness.

Applications

• Measuring the wet-film thickness of paint during application — comb, wheel or dial gauge (methods 1A–1C)
• Measuring the dry-film thickness of paint or varnish on steel and other magnetizable substrates — magnetic methods (7A, 7B; ISO 2178)
• Measuring the thickness of non-conductive coatings on aluminium and other non-magnetic conductive metals — eddy-current method (7C; ISO 2360)
• Measuring coating thickness on a cross-section or on a wedge cut (methods 6A, 6B)
• Measuring the thickness of an uncured powder coating layer (methods 12–14)
• Measuring coating thickness on rough surfaces (Annex B) and on wood (Annex C)

Key parameters

Standard

Standard number

PN-EN ISO 2808:2020-01

Title (PL)

Farby i lakiery — Oznaczanie grubości powłoki

Title (EN)

Paints and varnishes — Determination of film thickness

Step-by-step procedure

1. Choice of method

   Choose the method according to the kind of layer and the coating–substrate combination: on a magnetizable substrate — the magnetic method (ISO 2178), on a non-magnetic conductive metal — the eddy-current method (ISO 2360), for wet film — methods 1A–3.

2. Calibration or adjustment

   Before use, calibrate or adjust the instrument according to the manufacturer’s instructions with thickness reference standards on base metal similar to the test item; the instrument, standards and base metal should have the temperature of the test item (ISO 2360, 6.1).

3. Check at the place of inspection

   Check the calibration with standards at the place of inspection when the instrument is put into operation, after a change of material or geometry of the item, after a change of conditions (e.g. temperature) and periodically during use (ISO 2360, 7.1).

4. Measurement

   Measure according to the manufacturer’s instructions, taking into account the influencing factors from Clause 5 of ISO 2360 and ISO 2178: proximity of an edge, curvature, roughness, probe pressure and tilt, thickness and properties of the substrate.

5. Result

   Report the arithmetic mean of several measurements in a defined area and the standard deviation; unless otherwise agreed, take at least five measurements (ISO 2360, 7.2).

6. Test report

   Prepare the test report according to Clause 7 of PN-EN ISO 2808, stating the method used.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The available texts of the standards contain no safety requirements — working rules are set by the laboratory on the basis of a risk assessment

Frequently asked questions