I have old stucco on my house as well. It had latex paint over the stucco, then about 10 years ago it needed to be brightened up. I wanted latex again but the neighbors/painters that did the work suggested Thoroseal. I don't know the specific product, but it was dry in bags, needed to be mixed with water and painted on with large brushes. It turned out white and very nice.
Well now it needs it again. I would like some color this time and want a latex paint. The paint dealer knew nothing about Thoroseal and suggested a clear sealer type product from Sherwin Williams be applied first, then the latex. HELP. I don't want it falling off om walls in 6 months. Is this the right thing to do??