Deterioration of anti-corrosive paints by extracellular microbial products

Microorganisms are frequently found on deteriorated coatings and their deteriogenic action can be demonstrated by testing them against sound coatings of the same composition. No blistering or loss or adhesion occurred on either biocide containing coatings or coatings tested under sterile conditions. The mechanism of the attack is largely unknown. It has been assumed previously that to bring about loss of adhesion and blistering, the microorganisms must penetrate the coating and act from beneath the film. However, observations reported here indicate that microorganisms attack the coating from the surface thereby changing its chemical and physical properties. It has been demonstrated that these effects are generated by metabolites excreted by these organisms.