How to Repair Drywall Cracking Due to Humidity

Insert the thin edge of a 5-in-1 painter's tool into the crack if it is less than 1/4 inch in diameter. Widen the crack to at least 1/4 inch by scraping it out with the tool. Widening the crack makes the repair stronger.

Place a fine-grit sanding block directly over the drywall crack, and sand in the same direction the crack runs until the surface of the wall is smooth. Run your hand over the crack periodically to determine when it it perfectly smooth.

Take off the top of a small tub of joint compound. Insert a thin putty knife into the tub and scoop up 2 to 3 tbsp. of compound. Place the knife at the bottom of the crack and angle the handle of the knife upward. Pull the knife upward, smoothing the compound into the crack until it's covered fully.

Wait until the joint compound no longer appears damp, and then feel it to make sure it is hard. Sand the surface of the joint compound again with the sanding block until the area is flush with the remaining areas of the wall.

Look at the repaired area closely to see if the crack is gone. If you see even a hairline crack, apply another layer of joint compound, allow it to dry and sand it down.

Pull the top off a can of elastic crack coating. Shake up the can, and spray the entire area of joint compound with a light layer. Allow the product to dry completely.

Apply wall primer to the repaired area, using a paintbrush. Wait until the primer dries, and then touch up the paint, using a fresh paintbrush and a matching paint. If you no longer have leftover paint, you must repaint the entire wall.