The term “stucco” is use to describe many different surfaces these days. True stucco can sometimes be primed in as little as 15 days with specialized products, and under certain conditions. Stucco curing rates will vary, depending on temperature, air movement, and stucco type. We generally allow at least 30 days, and more is better. We must test the pH of the surface before we can actually say it is ready to coat. Certain coatings will tolerate highly alkaline surfaces, while some will usually fail. So test the pH to be sure, and make sure the coating you choose can handle You have a couple of options with respect to choice of coating systems. Stucco is a specialized surface, and your preparation of the surface, as well as your coating choice are extremely critical to the success, and long-term durability of your project.
Most standard paints and primers are inadequate to seal the pores of a stucco surface, even with multiple coats. You wouldn’t want to use latex paint as a primer. Most latex paint in addition to not tolerating the high pH of stucco, often exhibits pinholes in the coating surface due to the porosity of the stucco.
If the stucco is extremely porous, we might consider first sealing the surface with a siloxane/acrylic emulsion sealer. Siloxane chemically reacts with masonry to form a barrier to moisture intrusion, and serve as a foundation for our finish paint.
On dense stucco, consider a water-based pigmented ELASTOMERIC primer, then 2 coats of the highest quality 100% Acrylic house paint.
The coating system must be breathable, yet protect against moisture intrusion. The paint, however, is only part of the system. We must thoroughly inspect the surface for hairline cracks, stucco-to-wood gaps, and other areas of potential moisture intrusion. There are specialized caulking products for various functions. Caulking should be done after priming, and before painting. Many small cracks will become more visible after priming. The primer also increases the adhesion, thus waterproofing ability of the caulk.