Standard · Application and film thickness
ISO 19840
Measuring and accepting dry film thickness on rough (blast-cleaned) surfaces.
ISO 19840 says how to measure dry film thickness (DFT) on blast-cleaned steel and when a coat passes. It applies to nominal DFTs of 40 µm and above.
Gauge set-up and the profile correction
The gauge is verified at zero and with foils on smooth steel. A correction value for the profile is then subtracted from each reading: 10 µm for a fine, 25 µm for a medium and 40 µm for a coarse ISO 8503-1 profile, and 25 µm when the profile is unknown and no uncoated sample is available.
Sampling
The number of readings depends on the inspection area: 5 up to 1 m², 10 up to 3 m², 15 up to 10 m², 20 up to 30 m², 30 up to 100 m², then 10 more for each extra 100 m² or part of it. Areas above 1,000 m² are split.
Acceptance
- The mean of the readings is at least the nominal DFT.
- Every reading is at least 80 % of the nominal DFT.
- Fewer than 20 % of the readings are between 80 % and 100 % of nominal.
- No reading is above the specified maximum.
Note: ISO 19840 is outside the CIP 1 syllabus.
Use it: DFT acceptance calculator
14 practice items in the members area mention ISO 19840 (CIP 2: 6 · FROSIO written: 8).
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Also published openly: DeFelsko: ISO 19840 sampling plan and acceptance.
This page describes the subject of ISO 19840 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ISO. Checked on 2026-10-04; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.