The decrease in water accessible surface area drives the association of two large hydrophobic plates in both water and aqueous salt solutions: the contact configuration of the two plates possesses the minimum Gibbs energy in all cases. High charge density ions, having strong electrostatic attractions with waters, render more costly the process of cavity creation, as determined by classic scaled particle theory calculations, and strengthen pairwise hydrophobic interaction. Low-charge density ions, being preferentially bound to plate surfaces due to dispersion interactions, have to be removed to arrive at the contact configuration and weaken pairwise hydrophobic interaction. (C) 2010 Elsevier B.V. All rights reserved.