We have a semi-exterior wall with some spots where the paint is peeling and what appears to be dry, powdery plaster is falling out. The wall is under a roof so it's not rained on directly, but otherwise it is exposed to humidity and hot to freezing outside temperatures here in Virginia. It's a brick wall and I've seen no evidence of lathe. The other side of the wall is completely exterior and painted.
What's the best way to stop this and repair it?