Cover the entire stucco surface with one coat of primer. If the old stucco is stained, use a stain-blocking primer to keep the stains from bleeding through. The larger the stucco texture, the thicker the nap of the roller must be to effectively distribute paint into the crevices.. Apply a coat of exterior masonry primer to the stucco. Start by brushing the primer around the edges first and then roll on the primer with a thick-nap roller on the flat wall expanses.