Soluble Salts and Coating Failures

What happens when moisture and oxygen penetrate the coating Perhaps nothing, if a truly good bond has been achieved, but a number of reactions may occur. Where the moisture contacts the steel. 

Many contaminants, such as chlorides and other soluble salts, will actually enter into the chemistry of the cell to accentuate the attack. This is why many contractors are specifically requested to measure the level of these salts and continue washing a surface until the salt level is below an acceptable limit (Fig. 14.3). 

The rate at which diffusion of water and contaminants is occurring through a coating is largely controlled by its thickness and formulation. Based on empirical data, economics, and some theoretical considerations, the thickness of a coating necessary to resist moisture permeation from the atmosphere and otherwise resist deterioration is approximately 125 /J,m. 

FiauRE 14.3 Soluble salts detector kit (a) and sample being taken on a surface in preparation (b). (Courtesy of Termarust Technologies) 

All of these obviously produce a more rapid failure of the coating and 

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