Isocyanate-based materials have been used for decades as the basis for high performance adhesives, coatings, and primers. The origin of the excellent adhesion of these materials to metals such as steel has been generally assumed to derive from the condensation of isocyanates with metal hydroxyls to form metal oxide-cyanate esters analogous to urethanes. In this work Fourier transform infrared reflection (FTIR) was used to demonstrate that these esters do indeed form, but that the esterification is preceded by the formation of carbamate salts between the isocyanate and the hydrated metal oxide.