Is a primer required prior to applying Elastomeric Paint to a 5 year old stucco finish?
Normally an acrylic masonry primer is used to fill the pores then the elastomeric coating is applied. There might not be an actual requirement for a primer. This depends on the manufactures specs for the coating. If no primer is required and not used it will take more elastomeric to fill the stucco pores and give a proper build or mil thickness.
Check the coatings label or spec sheet for more details.