Is elastomeric paint capable of spanning hair line cracks between 2 dissimilar materials and prevent leaks? Stucco and a plastic stucco expansion joint.
Elastomeric paint can span hairline cracks between two dissimilar materials. How well depends on the elastomeric and its cured thickness, the thicker the better. One way to make sure you have no problems in the future is to first use a elastomeric patching compound over the crack and then apply the coating. One good patching compound is <a href="http://www.painters-toys.com/putty-and-spackle/exterior-spackle-and-patching.html" target="_blank">Dap's Elastopatch</a>, available as either smooth or textured to match the materials it's being applied to.