What common surface issue must be avoided to ensure good adhesion?

To ensure good adhesion of coatings to surfaces, it is essential to avoid a slippery surface. Adhesion relies on the ability of the coating to bond effectively with the substrate; a slippery surface can prevent proper physical and chemical contact between the coating and the surface.

When the surface is slick or has residues from oils, grease, or other contaminants, it disrupts the mechanical interlocking and surface energy interactions required for a stable bond. This can lead to issues such as poor adhesion, peeling, or flaking of the coating over time.

The other options, such as a clean and dry surface, a porous surface, and a textured surface, can all contribute positively to adhesion. A clean and dry surface ensures that there are no contaminants that could hinder bonding. Porous surfaces can provide additional mechanical interlock for better adherence of the coating, while textured surfaces can enhance bonding by increasing the surface area for the coating to grip onto. Thus, maintaining a non-slippery surface is crucial for achieving effective adhesion.