 My question is, when is the proper time to paint stucco? All right, so when you did the last painting project, did you use a primer on the stucco or did you just paint over what was there? I painted over what was there. I hear two things now that could have caused this condition. First of all, the primer is really important because the primer has properties that the paint doesn't, and specifically it has adhesive properties. So the primer is designed to grab on to that old surface and really bond to it, and then the paint is designed to flow evenly over the primer.