There are several reasons why a paint or coating can blister, depending on the type of coating, type of substrate, and the environment. In particular, the subject of this column is the blistering of a high performance epoxy maintenance coating.
Epoxies are one of the workhorses in the industrial maintenance industry.
They are two component coatings that must be mixed in a certain ratio prior to application, and subsequently cure by both solvent evaporation and a chemical reaction. A common variety, which is often used to line the interior of elevated potable water storage tanks, is the polyamide epoxy. One of the components of a polyamide epoxy contains a low molecular weight epoxy resin, while the other component contains a low molecular weight amide. When mixed together, the two components react to form a tough, densely cross-linked coating with good moisture and chemical resistance, and excellent adhesion to blast cleaned steel. Despite their good properties, polyamide epoxies have been observed to blister occasionally when subjected to prolonged water immersion.