The impact of ionic polymer cross-linking on the film formation kinetics of waterborne dispersions designed for use as acrylic pressure-sensitive adhesives (PSAs) was studied with Forster resonance energy transfer (FRET). Aluminum acetylacetonate (Al(acac)(3)) was added as an ionic cross-linker to a latex with un-cross-linked chains. The polymer interdiffusion (studied with FRET) suggests that the degree of polymer cross-linking in the wet dispersion is small, as the interdiffusion kinetics is similar to that of a latex with un-cross-linked chains only. Cross-linking mainly takes place when the film dries, and it is slower than interdiffusion; thus, a homogeneous film can be formed. Ionic cross-linking in the final film through Al3+ was proven by a large gel content and an increased cohesion, the latter evaluated with tensile and tack tests. Further aspects studied include the influence of serum pH on interdiffusion and cross-linking reaction and how ionic cross linking before film formation affects interdiffusion.