Electrical measurements in the study of immersed paint coatings on metal. I. Comparison between capacitance and gravimetric methods of estimating water‐uptake

An electrical capacitance method of estimating the water‐uptake of paint films on metal immersed in sea‐water has given, for many paint formulations, values agreeing with those obtained by a gravimetric method. For a few paints, however, pronounced disagreement was shown between values obtained by the two methods. Theoretical considerations show that such differences indicate, in general, a type of water distribution within the film departing considerably from the random, uniform distribution assumed in calculating the ‘capacitance’ values. Several types of distribution are discussed. The capacitance method can be used for routine testing of the water‐uptake of paints only on a type of paint known to give good agreement between the two methods; where applicable, it has decided advantages over gravimetric methods.