Holiday test is an inspection method used to detect discontinuities in painted/coated surfaces using specialized tools and equipment. These tools, called holiday detectors, are portable devices that are swept across the coated surface.
Holiday tests work on the concept of electrical conductivity. Metal substrates are excellent conductors of electricity, and therefore allow current to flow through them. On the other hand, many coatings are poor conductors of electricity and resist the flow of electricity. Using this principle, holiday tests use instruments to locate flaws in anticorrosive paints and coatings. A holiday test is also known as a continuity test.
In the coating industry, a holiday is a general term for various types of coating discontinuities, such as:
⦁ Runs and sags
These defects affect the coating’s thickness, thus revealing enough of the underlying metal to complete the circuit between the electrode and the grounding wire.