I do not know what this wall is made of, it’s a living room wall and the on the other side of the wall is the outside. I knocked on it and it sounded hollow so I tried a Zenith Sure Hook Picture Hanger (pic of the product attached) which as you can see did not work. Is anyone able to tell what picture hook product I should use? Adhesive strips are not an option, I need the hook to be secure.
