Remove the door. Use a hammer to gently tap the hinge pins up and out of the hinges. Lift the door off its hinges.
Clean the door casing. Wipe the entire surface of the door casing with a damp rag. Remove all dirt or grease that is on the wood prior to painting to increase the bonding capability of the new paint.
Fill any holes or dents. Apply spackling compound to any obvious dents and smooth with a finger or putty knife. Use fine 220-grit sandpaper to sand the area and even out the texture once the spackling compound is dry.
Caulk all cracks. Examine the casing and apply acrylic painter’s caulk to any visible cracks. Painter’s caulk dries quickly and can typically be painted one hour after application.
Protect the walls and the floor. Adhere painter’s tape to the walls around the casings to prevent paint from getting on the walls. Position a drop cloth in the doorway to catch any drips from above. Lay additional drop cloths on either side of the doorway to protect the area where the casings meet the floor.
Paint the casings. Stepping on a ladder, begin applying semigloss latex paint to the upper casing first with a paintbrush, starting at the inside of the casing and working your way out. Continue working your way out and down the side casings until you reach the floor. Use long brush strokes and continuously watch for paint drips, wiping them gently with the brush as they appear.
Remove the tape and drop cloths once the casings are completely dry, usually anywhere between one to three hours after painting is complete.