Hello – I will be painting my bathroom in the near future. In the past (last three times) when I painted it, the paint ran down the wall and had a hard time sticking to the drywall. My question is: Why does this happen? And what could I do to the wall to prevent this from happening again? I remember the last time I painted it was a royal pain in the rear to paint this small bathroom because the paint keep dripping off the walls (all over). Do you think I would have to sand the walls or put some kind of primer with texture on the walls to make the paint adhere to the walls. PLEASE HELP.