The polymers Epoxy and Poly(Methyl MethAcrylate) spin coated on Interstitial Free (IF) steel were subjected to external stresses and studied using the Delft Variable Energy Positron (VEP) beam facility. The polymer/metal interface was identified using an S-W map. After tensile experiments vacancy formation in the steel substrate was measured but no significant changes at the interface were observed. Positronium formation in the polymer layer was determined to be 30%. Results of application of the above method to a multilayer coating on an industrial can are presented.