This document discusses factors that affect the accuracy of high voltage testing of non-conductive coatings on concrete structures, including moisture content of the concrete substrate, thickness of the coating, and voltage level used. It notes that moisture content is critical for the test to work properly, and gives optimal moisture ranges. It also explains that tests done shortly after installation may not be accurate until moisture levels in the newly constructed areas have stabilized over time. A specific example is given where retesting found more issues after moisture levels increased over winter.