I have a job with a stair case wall that has an eggshell finish. We have pointed up the wall three times now. The latest time we primed it with "Equilizer" and pointed it. The wall was pretty much perfect, but two "air bubbles" have appeared. What is the cause of the air bubbles and can they be repaired with out redoing the entire wall? If not, how do I keep them from reappearing next time?