Standard · Adhesion, cure and holidays
NACE SP0188
Discontinuity (holiday) testing of new protective coatings on conductive substrates.
SP0188 sets how to find holidays in new coatings on conductive substrates such as steel. The 2024 revision changed how the spark test voltage is chosen.
- Low-voltage wet sponge for films of 500 µm (20 mils) or less. Use clean tap water, never salt water or deionised water. Above 250 µm (10 mils), add a low-sudsing wetting agent to make the test more sensitive, and wash it off before repair or the next coat. Without a specified setting, 67.5 V and 90 kΩ are typical.
- High-voltage spark above 500 µm, where it is the only method. It may also be used from 250 µm if the coating can take the voltage or the specifier allows it. The test voltage is 1.5 times the breakdown voltage of air at the measured DFT, plus 1,500 V: about 5.6 kV at 500 µm and 8.2 kV at 1,000 µm. This replaces the old rule of 100 V per mil, which let many coatings with holidays pass.
Test only a coating that has dried or cured, because solvent left in it gives false results. Check the voltage and the alarm on a known holiday before and after each period of use. Move the sponge or electrode at no more than 0.3 m/s (1 ft/s) over the whole area. Mark every holiday, repair it and test the repair.
18 practice items in the members area mention NACE SP0188 (CIP 1: 11 · CIP 2: 6 · FROSIO written: 1).
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Also published openly: DeFelsko: selecting the high-voltage holiday test voltage.
This page describes the subject of NACE SP0188 in our own words; it does not reproduce the standard. For the full text, buy the current edition from AMPP. 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.