I have an older house with a part sandstone exterior. Because of internal retention of damp, I have had plastic paint stripped from the sandstone, which is not in good repair. Is there a paint or other coating that will improve the appearance of the sandstone but allow it to breathe?

Go to your masonry supply House to get a sealer that seals in one direction and breathes in the opposite direction. There are many different grades also . Some as much as $100.00 per gallon. The Big Box stores won't really have what you need.