How do I fix a hole in a hollow door?
Most hollow core doors have solid wood frame that forms the top,bottom and sides of the door. Remove the molding on the field of the door so you have flat surface. Remove the doorknob. Cut A piece of luan or other smooth grained thin plywood the same size as the door. Cover the door in carpenters glue and apply the plywood. Drive a few nails around the perimeter to keep it in place until the glue can dry. With a hole saw drill out the doorknob hole using the old hole as a guide. Prime and paint to match the other side. reinstall the doorknob.