How to Replace a Interior Slab Door
Removing an old door from its hinges and hanging a new one is a fairly easy way to make a dramatic improvement in the look of a room. If your home has plain hollow-core doors, for example, replacing them with raised panel doors can make an enormous difference. While many doors are sold prehung—already mounted in frames for easy installation in new construction or remodeling projects—you can also find a wide variety of "slab" doors available at home centers and millwork outlets. A slab door is the best option if you want to hang a new door using the existing hinge locations and strike plate. This is considerably easier that the major carpentry work of tearing out the entire door and frame and installing a new prehung door.
Though it is not a difficult project, hanging a new slab door requires considerable precision to ensure that the hinges and doorknob/latch match up with the hinge locations and strike plate on the existing door frame. Patience is key to success.
What Is a Slab Door?
The term "slab door" refers to a rectangular door sold without any frame or hardware. It is the alternative to a "prehung" door, which is sold already mounted in a door frame. Slab doors can be made from solid wood, wood veneers around a hollow-core center, or fiberglass. They usually require that you cut mortises in the edge of the door for the hinges, and holes for the doorknob and latch. Some slab doors, however, may come with the door knob hole already predrilled.
Before You Begin
Slab doors come in many types, from very inexpensive hollow-core doors to solid hardwood raised-panel doors or leaded glass doors that may cost may hundreds of dollars. Whatever type you buy, hanging the door will be easiest if you buy one that is precisely the same size as the old door, as trimming down a door to a precise size is no easy task.
Many slab doors have no predrilled holes for the doorknob/lockset, which means you'll need to drill them yourself, as described below.
In our project, we will be mounting the new door on the same hinges used for the old door. You can also install new hinges, but this will work best if you select new hinges that exactly match the old ones. This will allow you to use the existing hinge mortises on the door frame.
When choosing a new doorknob kit, make sure to buy one with the same backset as the old doorknob. This information is printed on the doorknob mechanism, and is usually 2 3/4 or 2 3/8 inches.
What You'll Need
Equipment / Tools
- 3/4-inch wood chisel
- Small framing square
- Pry bar or lever substitute
- Cordless drill and driver bits
- 2 Spring clamps
- Hole saw
- Spade bit
- Slab door
- Hinges (if required)
- Doorknob/latch kit
Remove the Old Door
Carefully remove the door from the frame by removing the screws holding the hinges to the door frame. Be careful not to strip the holes in the wood door frame when removing the hinges. It helps to have a helper support the door as you unscrew the hinges from the frame.
With the door removed, unscrew the hinges from the edge of the door and set them aside.
Remove the doorknob from the old door. Also, remove the latch mechanism from the edge of the door by removing the screws. Look for a stamp on the doorknob mechanism indicating its backset measurement—usually 2 3/4 or 2 3/8 inches. Buy a new doorknob kit that matches this backset.
Mark the Doorknob Hole
Place the old door over the new door, with edges aligned precisely. Use a pencil to outline the location of the old door's doorknob hole on the new door.
Outline the Hinge Mortises
Place the old and new doors together on edge, with the hinge edges up. The tops and the bottoms of the two doors must match. Clamp them together with the spring clamps and make sure that they cannot fall over.
With a small framing square, transfer the dimensions of the old hinge mortises to the new door, marking them with a pencil. Not only do the mortises need to be correctly placed vertically, they must be stepped back from the face of the door by the correct distance.
Take care to be precise with this measuring/marking step, as it is essential to success.
Cut the Mortise Outlines
Cut the outline for each mortise by holding the blade of a sharp chisel along the outline and tapping the handle lightly with a hammer. The mortise should be exactly as deep as the thickness of the hinge plates.
Clear the Mortises
Tap a series of parallel lines about 1/4-inch apart along the interior of the mortise outlines. 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 bottom of the mortise. You may need to sharpen the chisel once again before doing this.
Test-fit the hinges to make sure they fit flush to the door edge. You can slightly deepen the mortises, if necessary, to make the hinges fit precisely.
Install the Hinges
Drive wood screws through the holes in the hinges to mount them to the edge of the door. Drilling pilot holes will make this work easier, especially with hardwood doors, but take care to keep the pilot holes small, as the screws need to grip tightly to ensure the door remains anchored securely to the hinges.
Mount the Door to the Frame
Position the door upright in the door frame to test the fit. It is helpful to have an assistant at this point. A pry bar under the door can be used to elevate the door so the hinges meet the door frame mortises.
Swing the door inward and open the hinge leaves to position them in the door frame mortises. Use the pry bar as a lever to adjust the door height so the hinges meet the receiving holes in the doorframe mortises. Drive wood screws through the hinges and into the door frame, then swing the door open and closed to verify the fit.
It can help to use longer wood screws when mounting the new door to the frame. This ensures the screws will bit into new wood and make them less likely to pull out.
Position the Doorknob Template
Tape the template that comes with the doorknob kit over the hole location you marked. The template will wrap around the door, providing the drilling locations for the doorknob hole and for the latch. Use a nail to mark the center points for the doorknob hole, and for the latch hole on the edge of the door.
Cut the Doorknob Hole and Latch Hole
Use a hole saw (usually 2 1/8 inches in diameter) and drill to bore the hole for the doorknob mechanism. Be careful to keep the hole saw perfectly perpendicular to the face of the door while drilling.
Then, drill a perpendicular hole from the edge of the door into the doorknob hole, using a spade bit This is where the doorknob's latch will fit.
Depending on the doorknob assembly, you may need to measure, mark, and cut an edge mortise with a chisel, so that the latch plate fits flush on the edge of the door.
Mount the Doorknob and Latch
Following the doorknob kit's instructions, insert the latch through the edge hole and secure it in place with wood screws. Make sure the plate is perfectly flush with the edge of the door.
Then, insert the doorknob spindle through the latch barrel, insert it into the opposite doorknob, and screw the doorknobs together.
Test the operation of the door.
Make Final Adjustments
With any luck, the doorknob latch on the new door will perfectly align with the existing strike plate on the door frame. If not, then it is an easy matter to remove it and replace it with the strike plate that came with the new doorknob kit. This may, however, requires some chisel work to enlarge or move the mortise where the strike plate fits on the door frame.
When to Call a Professional
This project has little tolerance for error. An expensive door can be easily ruined if you get the measurements wrong, even by a little bit. If you doubt your measuring and chiseling skills, it might be best to hire an experienced professional to do the work. A finish carpenter or handyman service is equipped to hang most types of interior doors and deal with any unexpected situations or issues that arise during the project.