The surface pressure of adsorbed layers of the cationic surfactants lauryl- and cetyltrimethylammonium bromide and ion exchange effects caused by the electrolytes sodium bromide and sodium acetate were studied at interfaces of water with air and methylated glass. New techniques used made possible a quantitative comparison of dynamic and equilibrium surface tension, wetting tension, and surface force (adhesion) isotherms and a control of surface purity. The surface activity is slightly higher at the interface with air than at the interface with the hydrophobic solid. In other respects, surface pressure isotherms for the two interfaces are similar. The methylated surfaces in pure water are effectively uncharged. Their mutual repulsion in solutions is due to ionic surfactant adsorption and is described at long distances by DLVO theory. At contact the interaction is always attractive but the adhesion is reduced according to the repulsive surface pressure contribution. The distance from which the surfaces jump into contact decreases with increasing surfactant adsorption at low surfactant and electrolyte concentrations. The decrease is correlated with the decrease of the contact angle rather than to van der Waals and double layer forces. As the surface pressure increases the wetting tension changes sign from negative to positive and the contact angle falls below 90 degrees. The jump-in distance becomes twice the thickness of the condensed monolayer. The barrier height changes according to the variation of the surface pressure. Sodium bromide increases while sodium acetate decreases the surface pressure of micellar solutions. In agreement with the ion exchange trend the contact adhesion decreases and increases accordingly. Exchange of bromide counterion for acetate leads to exceptionally large values of the negative surface activity.