It's time to wet, scrape and get dirty
Fill the weed sprayer with water (right out of your kitchen sink), and start spraying your ceiling. If you’re doing this by yourself, realize that you will probably need to spray down the whole ceiling twice before you even begin to scrape, and then again spray the area you are immediately working on.
You want the ceiling to be wet, not just moist or slightly dampened, so go crazy with that weed sprayer. Seeing how it only shoots small amounts of water at a time, it is going to take about 20 minutes to get enough water on the ceiling to be effective.