Wood doors are a beautiful accent to any room. Sometimes the wood in the door will crack because it couldn't move freely within the door panel. Wood needs to breathe, and if it is unable to do so, it may crack. You could buy a new door, but they can be costly. Instead, try to repair the door yourself. By sealing off the crack in your door, you will make your home more energy efficient. If done properly, the crack will disappear and the door will look almost perfect.
Remove the door from its frame and lay across two sawhorses or a table. Strip the paint or varnish that is on your door. There are several ways to do this. You can use a heat gun, a chemical remover or you can begin sanding the door with 80-grit sandpaper. You can do just the panel where the door is cracked, or you can sand the entire door.
Remove the sawdust and paint that the heat gun or chemical cleaners left behind by using a wet/dry vac. You can also brush the dust away. If you used sandpaper, sand the area again with 150-grit sandpaper. Vacuum the sawdust away or, if the door is outdoors, you can use an air compressor to blow the dust away. Sand the area one more time using 220-grit sandpaper. Vacuum or blow the dust away.
Wet a cloth and dampen the cracked area of the door. This helps to prepare the door to receive the wood patch.
Put a small amount of wood patch onto the tip of your putty knife. Press the wood patch into the crack. Leave the wood patch a little higher then the surface of the door. Try to match the wood putty with the colour of your oak door. Leave the wood patch to cure for 24 hours.
Sand the area with 220-grit sandpaper, moving over the area where the wood patch is covering the crack. Sand it until the patched section is level with the rest of section on the door. If you need to apply more wood putty, repeat step 3 and 4 until you are satisfied with the results.
Paint or stain the door. If you did just the one section, try to match the stain or paint as best you can. If you stripped the entire door, apply your choice of finish.
If you think you will have a problem matching the paint or varnish that is already on the door, it may be a good idea to sand the entire door. Try to match the wood putty with the colour of your oak door. Wear a respirator to protect your lungs. Wear protective goggles to protect your eyes.