Hollow-core doors are common in many homes. The doors are made with a thin sheet of plywood attached to a frame. The plywood splinters easily and most screws will pull out of the wood when they have any weight on them. Hollow-wall anchors, or molly bolts, spread the weight over a larger surface area behind the wood, preventing the hanging hardware from pulling out of the wood.
Hold the mirror in position against the door. Place a level on the top or side of the mirror to be sure it is level or plumb.
Mark the location for the hanging hardware. Position two equally spaced clips at the top and two equally spaced at the bottom of the mirror. Put a finishing nail in the hole on the clip and tap gently with a hammer to make a small hole in the wood at the location for the screws.
Gently drive the hollow-wall anchors into the hollow-core door with a hammer at the locations marked for the clips.
Put the hollow-wall-anchor screws into the mirror clip, then into the hollow-wall anchors. Tighten the anchors by turning the screws in a clockwise direction. When the clips are still loose, slide the mirror into the clips, then finish tightening the screws. Do not overtighten the screws or you will break the mirror. The mirror should be snug in the clips, not tight.
Hold the mirror in position against the hollow-core door. Measure the distance from the top of the door to the top of the mirror.
Place a piece of construction paper on the back of the mirror. Align the top edge of the construction paper with the top edge of the mirror.
Use a finishing nail to poke holes in the construction paper where the holes for the hanging screws are located on the mirror.
Hold the construction paper against the hollow-core door. Position the top of the construction paper so it matches the measurement from the top of the mirror to the top of the door.
Place a level on the holes for the mounting hardware in the construction paper. Move the construction paper so that the holes are level and centred on the door. Tape the construction paper to the door in position.
Place a finishing nail in the holes in the construction paper marked for the hanging hardware and tap gently with a hammer to make a small hole in the wood. Remove the construction paper.
Place the pointed end of a hollow-wall anchor in each location for the mounting hardware. Gently drive the anchor into the door.
Use a screwdriver to turn the screws in a clockwise direction, which will tighten the molly bolt against the inside of the door. Hang the mirror on the protruding screws on the door.
Hollow-core anchors come in a variety of sizes. Choose one that is rated to hold the weight of the mirror.