Hanging a door is a relatively easy project that is more about patience and precision than about mastery carpentry work. If you can drive a screw and use a wood chisel, you can probably hang a door.
Doors come either in pre-hung or slab form. Pre-hung doors are for new-construction or major remodel work where walls are being opened up. Pre-hung doors are shipped with their hinges already attached to a frame.
A slab door is a door only—no frame—that comes often with a pre-drilled hole for the doorknob but no insets cut into the side of the door for the hinges. These insets are called mortises, and they are necessary for the door to fully shut.
Remove the Current Door
If this is a door replacement, carefully remove the door by unscrewing it from its hinges. Next, remove the hinges from the door frame. Be careful not to strip the holes in the wood door frame when removing the hinges.
Match the Two Doors
Set both the old door and the new door side-by-side, with the hinge sides up. The tops and the bottoms of the two doors must match; any deviation means that the new door will not properly operate. Clamp them together with the spring clamps and make sure that they cannot fall over.
Mark the Mortise Cut Areas
With the Speed Square, transfer the dimensions of the old mortise to the new door, marking them with the pencil. Not only does the mortise need to be correctly placed vertically (as if the door were on-end and in place), it must be stepped back horizontally the correct distance.
Cut the Mortise Dimensions
If the chisel is not sharp, sharpen it on the whetstone. The chisel must be very sharp to produce quality work. Tap the chisel along the borders of the mortise marks. The mortise should be as deep as the thickness of the hinge plates.
Clear the Mortises
Tap a series of parallel lines about 1/4-inch from each other down the length of the mortise area. Then turn the chisel over, so that the angled side rests on the door, and chip out those 1/4-inch sections. When all of the sections are gone, go back with the chisel and flatten out the area. You may need to sharpen the chisel once again before doing this.
Install the Hinges
Drive screws through the holes in the hinges to mount them to the side of the door. If this is softwood or MDF, you can likely drive the screws without pilot holes. If this is hardwood, you should begin with pilot holes.
Inspect the Hinges
Make sure that the hinges are perfectly flush with the door. If you accidentally cut the mortises too deep, remove the hinges and add a layer or two of thin cardboard to raise the hinges until they are flush.
Mount the Door to the Frame
It is helpful to have an assistant at the point. Set the door up so that it is vertical. Move it close to the doorframe. Place the prybar under the door as a lever to raise the door high enough so that the hinges meet the receiving holes on the doorframe. Screw the hinges into place. Remove the lever and check the door swing.
Install the Strike Plate and Doorknob
Install the strike plate in the doorframe or leave the current one in place. Install the doorknob assembly in the new door.
Tips For Hanging a Door
For door replacements, make sure that the mortises on the new door exactly match those of the previous door. Any deviation may cause the door to shut improperly or to swing poorly.
Use a pry bar as a foot-operated lever to hang the door by yourself. Or rest the door on soft materials such as a folded shirt or sock.
If replacing a door, also remove the previous door's hinges from the door frame as they aid in cutting the new door's mortises.
When to Call a Professional
Hanging a door can be a complicated task if you doubt your measuring and chiseling skills. Also, this project has little tolerance for error. If a mortise is cut in the wrong location, it is difficult, if not impossible, to cut a new mortise. A general contractor or handyman service is equipped to hang most types of interior doors.