Water in any form is detrimental to the integrity of epoxy coatings systems. In fact, the presence of water, even in minute amounts, can cause ordinary epoxy coatings to fail. This is because water acts as a major obstacle for applied coatings to achieve complete adhesion and endurance against damages.
When moisture seepage has occurred in the regions between the coating and the coated surface, they weaken the adhesive properties of the entire coating system, resulting to visible blisters and cracks and a gradual coating failure.
Underwater epoxy coatings are designed to specifically address this problem, acting to displace any quantity of water within the surface, sealing it completely. Underwater epoxy coatings have a characteristic imperviousness to water. The presence or absence of water does not affect their chemical composition at all, which is a special polyamines formulation that is not moisture-attractive.
To understand this better, it is worth considering that ordinary coatings breakdown when exposed to water, because to these paints water is a solvent that leads to thinning out of the paint mixture. Often, too, the reaction of water to one or more components of the paint mixture can interfere with the curing process, leading also to eventual coating failure.