Flaws such as pinholes, air bubbles, inclusions, cracks, void and thin spots can occur in a wide range of coating material used in industry. A pinhole although small can cause extreme damage by permitting corrosive materials to reach the base material. Lack of continuity of coating causes premature failure, which can be very expensive to repair and lead to possible stoppages in production. In certain circumstances, an air pocket can represent a substantial portion of the total thickness, and thus cause a weak point, even though the coating is continuous.
High voltage Holiday Detectors are, in principle, insulation testers used to indicate a fault in the non-conductive coating under test be generating a spark which triggers audible and visual alarm.