You should wait at least 24 hours for drywall mud to dry before sanding or applying another coat. However, the exact drying time depends on several factors, including the thickness of the application, room temperature, humidity, and the type of compound used. Thicker layers, or projects in high humidity, may require 48 hours or more. Lightweight compounds tend to dry faster than heavier, all-purpose ones. You'll know the mud is ready when it feels completely dry and firm to the touch and has changed to a consistent light color. Sanding too early can cause smudging or gouges, so patience is essential for a smooth finish.

When sanding drywall mud, you’re going to create a very fine dust that may contain silica. Silica dust contains crystalline silica, which can cause long-term illnesses for people who inhale it in significant quantities. Wear a mask while sanding drywall. Then dampen a drywall sponge to wipe the dust off the drywall, helping to reduce the amount of dust that may become airborne.

On average, drywall installation costs around $2,000, with a typical range of $400 to $6,000, including materials and labor. The final price depends on several factors. The most significant is the size of the area, as many contractors charge per square foot. Other cost factors include the complexity of the job (e.g., cutting around multiple windows and doors, corners, or curved walls), accessibility, location, the thickness of the drywall, the height of the room, and the desired level of finish. The level of finish can range from simply hanging the drywall to taping and mudding the seams and painting the walls.

The short answer is yes, a sagging plaster ceiling is dangerous. Sagging plaster on a wall is something you should fix immediately, but it isn’t a major concern. If the same type of sagging occurs on a ceiling, however, you could be in danger of your ceiling falling in large chunks. When plaster sags, it loses its strength and ability to hold itself up. The bonds that hold it together are strong, though, so if a sagging area falls, it will take large pieces down with it.