Painting over mortar??

My old house has a stacked field stone foundation with a mortar coat on the outside. It has been painted forever, but the paint mostly flakes off. Are there any special tricks to make this job last?? Thanks for any help.

 

Paint should adhere ok

When it peels, does it peel down to raw stone/mortar or are there multiple layers of paint peeling? One common problem when painting masonry is chalky paint. Cheap paint or even good paint that has been on for a long time tends to get chalky with age. Paint won't adhere well to chalk. The chalk either needs to be removed and if that's not feasible, emulsa bond should be added to the 1st coat of latex paint to help with adhesion.

Moisture can also affect adhesion. If moisture is running over or thru the foundation it will make it hard for paint to last.

 

It peels all the way back to mortar. I'll ask my paint store about emulsa bond. I suppose that moisture moves thru the wall even though this is a dry climate. The dirt in the crawl space is pure dust.