Some tips on replacing exterior door frames are to completely remove old paint and caulk, carefully pry away the door frame and use wood nails in conjunction with wood putty when installing the new frame. It’s best to use a utility knife to cut away old paint and caulk around the door frame where it meets the door jamb, siding and miter joint.
Once the paint and caulk is removed, the repairer can pry away the door frame with a flat crow bar. He can ease the process by cutting the door frame in portions with a saw.
To find the proper length of the two vertical and one horizontal casings, the repairer can measure the length and height of the area around the door. He should cut lengths longer than what is needed; holding the lengths in place, mark where the cuts should be made. This method is more accurate than other measuring techniques.
The repairer can use wood nails in conjunction with wood putty so that the new frame stays securely in place while the putty dries. Sometimes only one portion of a door jamb needs replacing. In that case, the repairer should reinforce the undamaged portions with finishing nails prior to removal of the damaged section.
The repairer can prevent door frame rot by using plastic door frames. Wood door frames should be treated with wood preservatives at the end grain prior to installing the molding.