Wetting is the spreading of liquid over a solid substance. The adhesive and the substrate are held together by lots of weak electrostatic forces. This means that for maximum adhesion, the adhesive should be completely spread over the substrate to increase the contact surface area between the two substances. The wetting of an adhesive is its ability to form an interface with the solid surface. The degree of wetting, also known as wettability, depends on both the surface tension and the viscosity of the adhesive.