The quality and useful life of anti-corrosion painting is determined by several factors, pre-treatment and protection of treated surfaces against moisture are the most important factors. Surfaces that have been blasted are completely unprotected against corrosion and must not be subjected to excessive humidity or to the risk of condensation. The rate of corrosion is high above a certain value of the relative humidity – the critical humidity. Below the critical humidity the corrosion rate is negligible. The critical humidity is about 60%, but it should not exceed 50% in practical situations. In practice, it has been found that dehumidification is a crucial factor for anti-corrosion painting. The cost of dehumidification is only approximately 4% of the total treatment cost of corrosion preventive painting of a ship’s tanks. Moreover, de-humidification is often a pre-requisite for the correct execution of anti-corrosion painting. This is especially crucial in the painting of blasted surface of a ship’s tanks.