Holes in hollow core doors are problematic to be certain, but often, repairing the hole is a viable option over replacing the entire door. Keep in mind, if the door has been painted, the repair job will be easier to camouflage than if the door has a natural wood finish.
Step 1: Begin by removing any loose material around the hole. Use a carton knife to cut away rough edges or splintered material.
Step 2: Once the hole is free of loose material, sand the area to be repaired with a 100-grit sand paper.
Step 3: If the door has fiber board filling, you may be able to fill the void behind the hole with some minimal expanding spray foam insulation. Use a small amount of foam to fill the hole, adding a little at a time to avoid over filling. Once the door has been filled, use a carton knife to cut away any excess foam. Ideally, the foam should be level with the inside edge of the door surface material. Sand the opening smooth and proceed with patching.
Step 4: If you are unable to fill the void behind the hole with spray foam insulation, purchase a metal drywall patch and adhere it to the face of the door over the hole. If the patch is not self-adhesive, use a small amount of wood putty to hold it in place.
Step 5: Once the hole has been filled, whether with spray foam or a drywall patch, you are ready to cover the imperfection. Choose stainable wood putty or for natural wood doors, choose colored putty that most closely resembles the existing finish.
Step 6: Use a flexible putty knife to spread the wood putty over the patched area. Lightly feather the putty out from the hole to allow a seamless transition from the patch to the natural finish.
Step 7: Once the putty has cured, sand it as smooth as possible. Apply a second coat of putty if needed and allow to dry.
Step 8: Sand the patched area with fine grit sand paper until smooth. Use a tack cloth or rag soaked in mineral spirits to wipe away any dust and residue.
Step 9: After the putty has dried completely, paint or stain the area to match the existing finish.