Our fabulous plaster guy tore to our aid after that freaky rain/sleet/snow occurrence just before Halloween. The plaster hadn't cured yet and this was the result. He was just as nice as could be and promised to fix it. The manufacturer recommended a vinegar wash, and if that didn't work, a wash of diluted muriatic acid.
It is VASTLY improved. (It's raining in this photo, so the walls look a bit more irregular in color than they usually do.) He might still need to do some touchup in the Spring, but this is so much better!
And I don't think I ever posted a photo of the completed walls in the carport - same plaster treatment as in the courtyard, but this was completely cured and is also protected from above from freaky weather.