I was told that a house needs to breath to eliminate moisture (mold). Will elastomeric paint allow this to happen or will it keep the moisture from exiting the building and trap it inside.
Yes a house does need to breath. This air exchange can and will lower moisture levels inside an exterior wall. All paints and coatings slow down water vapor from leaving the walls.
Many elastomeric paints do allow good air exchange. You can find this out by reading the specs for different elastomeric paints. Look at the part that says 'Water Vapor Permeance'. The higher the number the more water vapor that can pass through.