Definition - What does Sagging mean?
Sagging is the tendency of a wet coating to flow downward due to the force of gravity, which produces a thicker lower edge on the surface being coated. Thicker and denser coatings are less likely to sag.
Corrosionpedia explains Sagging
Sagging is problematic because it may cause coat wastage, ineffective corrosion protection efforts and increased wear and tear in moving systems. Sagging can be reduced by the use of an anti-sag agent.