A hole in a hollow door is not always difficult to repair. Large doors might need to be replaced if the hole has caused noticeable cracks to appear across the surface that are more than an inch or two long. Smaller holes can be patched in one of three ways depending on the door and the supplies available.
Prepare the Area
The first step is to prepare the area by using a sharp utility knife or a sharp chisel to cut away splinters and form a solid edge. This will ensure the patch can attach firmly to the door. Sometimes cutting angled and irregular shapes will make the patch less noticeable than creating an identifiable pattern like a square.
Spray Foam Insulation
The first method that can be used is to fill the hole with spray foam insulation. The insulation will slowly expand inside of the hole and then cure into a solid substance. The floor should be protected with a drop cloth or newspaper since the spray insulation is likely to leak at some point. Any cured insulation that is sticking out of the hole can be scraped away with a knife or chisel. The surface can then be sanded down until it is level with the door.
Metal Drywall Patches
Another option is to purchase metal drywall patches that are self-adhesive. These are fine metal meshes. The mesh can be cut so that it is just a little larger than the hole in the door. The patch is applied and allowed to cure. The patch will create a good base for a final coat of wood putty.
Using Putty to Hide the Repair
Both spray insulation and drywall patches can be hidden by applying a layer of stainable wood putty. The putty should be spread across the patch and allowed to cure before being sanded flat. The putty can then be stained or primed and painted. This is an effective way to hide the repair so that it is less noticeable.
Veneer doors can be patched differently. It is possible to carefully cut away a small portion of the veneer around the prepared hole. A template can be made of the shape. A patch is then cut from a new piece of matching veneer. The patch can be glued into place with wood glue. The patch can be sanded around the edges and then stained to match the finish of the door.