I have a house that was built in 1980. We decieded to take down the original popcorn ceiling and replace it with "knockdown. The knockdown texture didn't seem to stick very well to the existing drywall. We took as much of the loose stuff off as possible with a broom and then painted it. Now there are still some places that don't look so good. Any ideas on how to repair those spots. Maybe take a scraper and scrap the high spots and then touch up with paint????