ASTM G9-07(2013)e1

4.1 The deterioration of an insulating coating film is intimately related to its moisture content. The water penetration test provides a means for monitoring the passage of moisture through a coating material by means of changes in its dielectric constant. When expressed in relation to time, the test data will reflect a rate of deterioration which is a characteristic of the coating material and will bear a relation to its expected useful life as an insulating coating. The test for water penetration will also provide information that is useful in establishing the optimum coating thickness for a given material.