A preparatory coat of paint is a layer of paint applied to a surface before the main coat. The most common type of preparatory coat is a PRIMER, which is a paint that seals and prepares the surface for the main coat. PRIMER is typically made up of a combination of resins, solvents, and pigments. It helps to create a strong bond between the surface and the main coat, and it also helps to protect the surface from moisture and other elements.