Adhering a Mirror

Gluing works well wherever you want to protect tiles, plasterboard or older plaster that crumbles when drilled. A mirror without screws looks clean, and its weight spreads over a larger area instead of resting on two or four points. For a normal bathroom mirror it is a reliable and fairly quick solution.

Keep in mind that a glued mirror is practically permanent. You cannot move it a few centimetres later. Taking it down is hard work and can damage the wall behind it. So plan the position first: height, distance from the basin, lighting and sockets.

Adhesive on its own is not the right choice in these cases:

• Very large or heavy mirrors, roughly above 15 to 20 kg or above the adhesive manufacturer's limit. Here the adhesive is combined with a bottom support rail or a hidden mechanical fixing
• Weak surfaces such as flaking paint, wallpaper or damp, sandy plaster
• A mirror you may want to move later, where hooks or brackets are more practical
• Smooth plastics and some laminates, where the adhesive may not bond well. The adhesive manufacturer's information decides

The most important thing is to use an adhesive that is clearly labelled as suitable for mirrors. A mirror has a thin reflective layer on the back, protected by a coating. Ordinary acetoxy silicone, which you can recognise by its vinegar smell, and adhesives with strong solvents attack this layer over time. Dark spots then appear on the mirror, and they cannot be removed.

In practice, mirror adhesives based on MS or hybrid polymers are the usual choice. They hold well even in a damp bathroom and stay slightly flexible, so they cope with small movements of the wall as the temperature changes.

For the wall itself there is one simple rule: it must be firm, dry, clean and as flat as possible.

• Plaster and plasterboard: both take adhesive well, but fresh plaster must dry out fully, and a dusty surface is best treated with a primer first
• Ceramic tiles: you can glue onto them if the tiles are firmly fixed and degreased, because grease and soap residue greatly reduce adhesion
• Painted walls: the mirror only holds as well as the paint under it. If the paint is peeling, it has to come off

For a bathroom, a mirror with a safety film on the back is a good idea. If the glass ever cracks, the film keeps the pieces together.

A small mirror on a flat, dry wall takes very little time. The job gets longer and more involved mainly when:

• The mirror is large and heavy and needs two people to handle it
• The wall is not flat and has to be levelled first
• An old glued mirror has to be removed and the wall cleaned
• Damaged tiles need replacing or repairing
• The mirror needs a hole or cut-out for a socket or switch. The glazier makes this when the mirror is produced, as it cannot be done on site
• A bottom support rail or hidden mechanical fixing is being fitted

If the mirror is light enough for you to handle alone and the wall is flat and solid, you can do this without previous experience. For larger, heavier mirrors, get a helper or call a tiler.

1. Read the instructions on the adhesive, especially the curing time and suitable surfaces.
2. Mark the position of the mirror with a pencil and spirit level, including the bottom edge.
3. Clean the wall, degrease tiles with spirit and let everything dry completely.
4. Fix a temporary support under the bottom edge, for example a batten held with tape, or packers.
5. Wipe the dust off the back of the mirror.
6. Apply the adhesive in vertical strips a few centimetres apart, not over the whole surface and not right up to the edges.
7. Stand the mirror on the support, place it against the wall and press evenly with your palms.
8. Check the position with the spirit level while the adhesive still allows small adjustments.
9. Secure the mirror to the wall with tape and leave the support in place for the full curing time stated by the manufacturer, usually at least a day.
10. Remove the tape and support and, if needed, fill the bottom gap with a suitable neutral sealant.

Why should the adhesive not cover the whole back? Air needs to move behind the mirror and moisture needs a way out. Adhesive spread over the full surface also cures slowly and unevenly. Vertical strips let any moisture run down and dry.

Other mistakes that come up again and again:

• Using ordinary silicone or a general construction adhesive instead of a mirror adhesive
• Gluing onto a dusty, greasy or damp wall
• Leaving the mirror without support, so it slowly slides down while curing
• Sealing the whole edge with silicone, which stops the back from ventilating
• Fixing a heavy mirror with adhesive alone, without any mechanical support

• The mirror is level and in the agreed position
• It does not flex or move when you press gently on the corners
• No adhesive is oozing out at the edges and the glass is clean
• There are no scratches, chipped edges or spots on the reflective layer
• Cut-outs for sockets and switches line up and the mirror does not touch any wiring
• On a heavier mirror, the bottom support or mechanical fixing is visible or documented
• You have been told when the adhesive fully cures and from when the mirror can be cleaned normally