Hi Karen, Try a stain killing primer under your color coat (Zinssner makes a good one). This stuff is actually a pigmented shellac that seals the wall or ceiling. It's generally used for bathrooms to seal out moisture and prevent mildew. I've read that it also works as a vapor barrier. I've been using it as a primer to seal my old horse-hair plaster walls and it seems to work. But you've also got to seal up all the outlets, around the baseboard moldings, etc to actually form an effective vapor barrier.