The paper focuses on the fundamentals of surface preparation as a critical part of a process in order to gain a surface for the mechanically adhering coatings. In more detail the roughness of the surface is cross sectioned looking at the peak and valley distribution or density. Coatings primarily need to "wet" the surface flooding the valleys but difference in viscosity need a different peak density in order to allow for the wetting.
In the paper, examples of different peak densities and coating viscosity will be used.
Surface cleanliness is often specified and related to various standards but due to the difference in adhesion mechanisms of the coatings there is no assurance adhesion will be achieved just by cleanliness, roughness is the key that can make a coating work or flake off.
As they say, a coating is only as good as the surface preparation.