This article comes from The Spruce.
Large mirrors multiply the sense of space in rooms and add light to a dark room. Yet large mirrors or mirrors with elaborate frames also are inherently heavy. When you hang a heavy mirror, you need to get it right the first time. While other items might sustain minimal damage if they accidentally drop, most mirrors will shatter and cause a huge mess if hung improperly.
Mirrors are heavy because mirrors are made of glass; any framework only adds to the overall weight. Most wall systems are constructed with vertical wall studs placed every 16 inches on-center, with 1/2-inch drywall laid across the studs and held in place with drywall screws or nails.
To hang a heavy mirror on a wood stud wall system, it is always best to identify the location of one or more studs behind the drywall and to drive the supporting fastener into those studs. Mirrors and pictures are sometimes hung directly from drywall but this is an inferior method that may result in the fastener pulling out of the wall.
Hang heavy mirrors either with screws and hanging wire or with metal cleats:
Heavy mirrors that have a metal wire can be hung on wood wall systems with one or two screws driven into wall studs. If possible, be sure to use two screws. Purchase only braided stainless steel wire intended for hanging mirrors and pictures.
Metal cleats are a stronger alternative to the wire-and-screws method of hanging heavy mirrors. A metal strip is installed on the back of the mirror, with an interlocking cleat installed on the wall. Installation must be precise since you do need to make sure that the wall cleat is exactly level as it cannot be adjusted.
If you wish to double-check the strength of your wall fastener, purchase a digital hanging scale (not a bathroom scale), hang the hook on the fastener, then manually pull the scale to the weight of the mirror or more.
Do not use drywall screws as supporting fasteners since they are brittle and may snap.
Use the stud finder to locate the positions of the studs near your intended installation area. Mark the positions with a pencil. In most cases, studs should be located every 16 inches, on-center.
With the pencil, mark the vertical location of the heavy mirror. Keep in mind that the top edge of the mirror will generally be 2 inches to 4 inches higher than the marks, so take that into consideration.
Cast a laser level line across the two marks and adjust the marks so that they are level.
With the cordless drill, drive two fastener screws on the adjacent studs. The heads of the screws should protrude about 1/4-inch.
Drape the mirror’s stainless steel hanging wire across the two fastening screws and let the mirror hang. Adjust the level by sliding one side of the mirror either up or down.
Use the stud finder to strike a level line where you want the cleat to run. Be precise about this, since cleats do not allow for re-adjustment in the way that the wire-and-screws method does.
If you have a 16-inch or longer cleat, it can span from one stud to an adjacent stud. If the cleat is shorter than 16 inches, screw the center hole to a stud and screw the two end holes into drywall anchors.
Screw the other cleat into the top of the frame on the back side. Be sure to keep the cleat parallel with the top of the frame.
Attach the mirror by sliding the mirror cleat over the wall cleat. The mirror should rest firmly in place.
For antique mirrors, overly heavy mirrors, some masonry walls, or if you simply do not feel comfortable hanging a heavy mirror, call a handyman service. This basic project should take less than an hour for most mirrors and wall systems, and about a half-hour extra for masonry walls.
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