Solvent-free epoxy resin based coatings have been applied and left for 24 hours at room temperature for initial setting under dry conditions. The curing process of the coatings was then completed at different relative humidity conditions. Meanwhile internal stress development was monitored as a function of time using the restrained beam deflection technique. Internal stress build up in solvent-free epoxy coating during the post-curing process was found to be highly dependent on the degree of relative humidity (RH) and the type of the curing agent. The development of tensile internal stress during the curing process of the different epoxy coatings took place only under low relative humidity atmospheres (<10-30%, depending on the curing agent), whereas compressive internal stress advanced at higher relative humidity conditions.