Deep cracks in plaster walls or ceilings typically are caused by age or issues with setting the plaster upon installation. Whatever the reason, it is possible to repair the plaster cracks with a few items available at your local home improvement store. The task should only take a few minutes to complete and no home repair craftsmen are needed.
Apply mesh tape over the crack.
Sand down the area around the crack. This removes all loose plaster that may stick during the repair process.
Mix the joint compound with water in a bucket.
Dip your 4-inch knife into the mixture and apply a 1/8-inch layer over the crack, covering the tape.
Smooth out the area with the knife, making sure the tape is completely covered with the joint repair mixture. Wait for the mixture to completely dry. You know it is dry when the mixture is hard.
Apply a second coat of joint compound over the initial layer. Allow the second coat to dry, then sand off any high areas of the joint compound that protrude from the crack.