Why is moisture content important for coatings?

Most resin coatings (Epoxy, PU) are moisture-sensitive. If applied to damp concrete, they will bubble, blister, or delaminate. We measure the moisture content of the substrate using a hygrometer or carbide bomb test. If the moisture is too high (typically above 4-6%), we must use a specialized moisture-tolerant primer or wait for the substrate to dry. Ignoring moisture content is a leading cause of coating failure.