Which of the following is NOT one of the essential requirements for a satisfactory tack coat application?

In the context of tack coat applications, the essential requirements focus on surface preparation and application methods to ensure proper adhesion between layers of pavement. Thoroughly cleaning the surface is critical because it removes dirt, debris, and any contaminants that could impede the bonding of the new layer. Uniform coverage is also vital to make sure the entire area receives the same treatment, preventing weak spots that could lead to issues later. Ensuring the proper rate of application ensures that there's enough tack coat for effective bonding without excess material that could cause problems.

Using a special cleaning agent is not considered an essential requirement as general cleaning methods, such as sweeping or washing with water, may often suffice to prepare the surface for tack coat. Therefore, this option does not align with the core principles necessary for a satisfactory tack coat application.