After a protective coating has been applied, it is important to ensure there are no defects or discontinuities present that expose the substrate beneath. Small areas of thin or missing coating, called 'pinholes' or 'holidays', can become foci for corrosion and drastically reduce the life of a protective coating system. A holiday detector is a non-destructive instrument used for detecting these discontinuities. Other names include porosity detector, continuity tester, and holiday tester.
DeFelsko offers two types of porosity/pinhole detectors: low voltage (wet sponge) and high voltage (spark tester). Low voltages detectors, like the PosiTest LPD, are typically used on coating systems less than 500 µm (20 mils) thick. High voltage spark testers, like the PosiTest HHD operate at voltages up to 35,000V and are typically used on coatings more than 500 µm (20 mils) thick.