Linear polyurethane paints have proven to be the most durable protection over epoxy. Regardless of the paint system used, thorough preparation of the surface is essential for good paint adhesion and a smooth finish. For coating, follow the paint manufacturer’s instructions.
Wet-sand the surface to remove any flaws and provide a texture for the paint to key into. If you are using a filling or sandable primer, use 100 grit paper. Use 220-320 grit paper if no primer is used. The thinner the paint film thickness, the finer the grit of sandpaper needed.
Rinse the surface with clean water and dry thoroughly. The rinsed surface should not bead or fish-eye. Both of those phenomena could be a sign of local contamination. Re-wash the surface with solvent if necessary and wet-sand. Allow the surface to dry thoroughly before you start painting.