We let the girls color all over the unfinished drywall, thinking we were cool parents and OUR folks would never have let us do that. And then we primered and primered and painted and grey primered and grey primered and painted ONLY to find that the marker STILL bled through. Ace Hardware's guy came through, though...He said to paint a layer of shellac over the marker and the problem would stop. I did and it did. Whew!