Walls and Ceilings - plaster ceiling in bathroom

The bathroom ceiling is plaster from about the 1930's it's in good shape but when I moved in the house it had mildew mostly above the shower. We installed a exhaust fan. I cleaned the ceiling with bleach, scraped and sanded it. I then painted it with a two coats of Kilz and a water resisdent paint. It was fine for about a year. The paint is now peeling above the shower and a few places have mildew again. Maybe because the Kilz was old?? We recently added another vent to the attic and new siding (due to the complements of a tornado). With the new vent in the attic and if I redo it with new Kilz and Paint do you think it will fix it??? Any ideas??

And add a mildewcide from the paint store to the paint.
Good luck!
Mike

My feeling is that if you were to paint it with Kilz, then next year you'll be doing the same thing again. You need to determine the cause of the mildew. Tearing out the lathe and plaster is a possible alternative you should consider.