The first cause of this is termite defense. Stucco which is applied over a Wooden frame wall have to have a separator sheet guiding the metal wire mesh that functions like a the base for stucco application along with the wall down below. Stucco alone is just not a https://www.termitehq.com/stucco-termites-how-to-spot-prevent-and-eliminate-hidden-infestations-in-your-walls/