Variety of Epoxy Paints

The number of epoxide reactions possible is practically infinite and has resulted in a huge variety of epoxy polymers. Paint formulators have taken advantage of this variability to provide epoxy paints with a wide range of physical, chemical, and mechanical characteristics. The term epoxy encompasses an extremely wide range of coatings, from very-low-viscosity epoxy sealers (for penetration of crevices) to exceptionally thick epoxy mastic coatings. 

Mastics are high-solids, high-build epoxy coatings designed for situations in which surface preparation is less than ideal. They are sometimes referred to as surface tolerant because they do not require the substrate to be cleaned by abrasive blasting to Sa2 1/2. Mastics can tolerate a lack of surface profile (for anchoring) and a certain amount of contamination (e.g., by oil) that would cause other types of paints to quickly fail. 

Formulation is challenging, because the demands placed on this class can be contradictory. Because they are used on smoother and less clean surfaces, mastics must have good wetting characteristics. At the same time, viscosity must be very high to prevent sagging of the very thick wet film on vertical surfaces. Meeting both of these requirements presents a challenge to the paint chemist. 

Epoxy mastics with aluminium flake pigments have very low moisture permeations and are popular both as spot primers or full coats. They can be formulated with weak solvents and thus can be used over old paint. The lack of aggressive solvents in mastics means that old paints wiU not be destroyed by epoxy mastics. This characteristic is needed for spot primers, which overlap old, intact paint at the edge of the spot to be coated. Mastics pigmented with aluminium flake are also used as full-coat primers. 

Because of their very high dry film thickness, build-up of internal stress in the coating during cure is often an important consideration in using mastic coatings. 

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