Repair

• 1). Fit the wooden pieces of the door jamb back together as best you can. Hold them in position with finishing nails. If possible, hammer the nails into solid wood.
  
  
• 2). Fill cracks with wood filler. Smooth the filler into cracks with a putty knife and allow the filler to dry to the touch.
  
  
• 3). Sand the rough edges of the wood filler away. Paint or stain the repaired door jamb to further cover the damage.
  
  

Replace

• 1). Remove the weather stripping on the door if the door is an exterior one. Use a pry bar to pry off the molding on the door near the door jamb. Set the molding aside to use again.
  
  
• 2). Hold a circular saw against the door jamb. Cut along the edge of the door frame. Cut the last few inches on each end of the door jamb with a hand saw. Pry the door jamb away from the door. Discard the old door jamb.
  
  
• 3). Measure the width of the door jamb. Use a ready-made door jamb if you can find one the right size. Use a piece of 1-by-6-inch pine to make a new door jamb if you can't find a ready-made jamb. Cut it to the right size with your circular saw.
  
  
• 4). Hold the new door jamb in place along with a level to make sure it's plumb (vertically level). If necessary, add wood shims behind the door jamb to make it plumb. Use 2-inch finishing nails to hold the door jamb in place. Nail them in several positions to hold the door jamb firmly.
  
  
• 5). Drill a hole for the striker plate of the door's lock. Position the striker plate over the hole. Screw the striker plate into the door jamb.
  
  
• 6). Caulk the door jamb with silicone caulking. Attach new weather stripping to the door jamb. Put the molding back on the door frame.
  
  
• 7). Paint or stain the door jamb. Allow it to dry before giving it a second coat of paint or stain.