Mirrors cut to size, to the millimetre

What matters when you order mirrors cut to size in London

Mirror is float glass with a coating on the back, and almost everything that goes wrong with it comes from that one fact. People ordering mirrors cut to size in London usually concentrate on the two figures that are easy to picture, the dimensions and the price per square metre. The things that actually decide whether the panel still looks right in ten years are the thickness, the edgework, the grade of the backing and the way it is fixed to the wall. None of those appear on a one line quote, so nobody argues about them until the mirror is already on the wall.

We cut, grind and polish mirror in our own workshop in Wembley, so the panel that arrives at your house has been measured, cut, edged and inspected by the same firm that fits it. That matters more with mirror than with ordinary glass, because a mirror puts its own faults on display. A pane of clear glass with a slight wave in it still looks like a window. A mirror with a slight wave in it looks like a funfair.

How is a mirror actually made?

A mirror starts as a sheet of ordinary float glass. It is washed, polished with cerium oxide, chemically sensitised, and then silver is deposited onto the back out of solution. That silver film is the reflection and it is a fraction of a micron thick. On its own it would tarnish in weeks, so a second metallic layer goes on top, historically copper, now more often a copper-free passivation chemistry. Over that go two or three coats of protective backing paint.

So the back of a mirror is a stack: glass, silver, a protective metal or passivation layer, then paint. The paint is the only thing standing between the silver and the air. Scratch it with a screwdriver while you are fitting, or let water sit against it, and the silver underneath will start to go. That is why a mirror which has been dropped flat and looks fine can develop a grey bloom six months later.

Are the better grades of mirror worth paying for?

Mirrors for internal use are covered by BS EN 1036, which includes requirements for the silvering and for resistance to corrosion. Above that baseline, manufacturers sell higher durability mirror with copper-free backing and heavier paint systems, tested in salt spray and humidity cabinets. Those grades genuinely last longer where there is moisture or cleaning chemical in the air.

Where they are worth the money is a bathroom, a shower room, a utility, a kitchen splashback run and a home gym, because gyms get wiped down with disinfectant every day. Where they are not worth the money is a dry hallway, a bedroom, a living room alcove or a home office. If your wall never gets wet, standard grade silvered float mirror is the right buy and the premium grade will look identical for the whole of your life in the house.

A mirror on a dry internal wall does not need an upgraded backing. Buy the right thickness and the right edge instead. That is where the money shows.

Why does thin mirror in a large panel look distorted?

Float glass is flat, but it is not perfectly flat, and it bends. Hang a large thin panel on a wall that is not dead flat and the glass will take up the shape of the wall, or bow in the middle between its fixings. In a window you would never notice. In a mirror you notice immediately, because the light travels in through the glass and back out again, so any curvature in the surface is applied to the image twice over. A bow you could not detect with a straight edge turns a reflected door frame into a banana.

Thickness is the fix, because stiffness rises very steeply with thickness. Going from 4mm to 6mm roughly triples the panel’s resistance to bending. Our rule of thumb is that anything over about a metre in either direction, anything a person will stand in front of at full height, and anything in a gym gets quoted in 6mm. Below about 600mm square, 4mm is perfectly honest and we will not try to sell you 6mm for a cloakroom panel.

The other half of the fix is the wall. A 6mm panel bonded flat onto a bowed plaster wall will still be pulled out of true. On old plaster we either batten and ply the area first to get a flat plane, or we pack and mechanically fix so the glass is allowed to stay straight while the wall stays crooked.

How should a large mirror be fixed to the wall?

Weight decides this, and the weight is easy to work out. Glass runs at about 2.5kg per square metre for every millimetre of thickness, so 4mm mirror is roughly 10kg per square metre and 6mm is roughly 15kg. A 2000mm by 1000mm panel in 6mm is therefore about 30kg of glass hanging off your wall with nothing underneath it. That is a weight nobody would expect to hold up with sticky pads, and yet that is what a lot of mirror adhesive is being asked to do.

• Mirror adhesive on its own: sensible for small and medium panels on sound, flat, solid plaster or ply. We stop relying on adhesive alone once a panel is heavy enough that a failure would be dangerous, and we always prefer a bottom support to carry the dead load.
• Mirror clips, J-channel or a bottom track: the honest workhorse. The panel sits on something, so the fixings are only restraining it rather than carrying it. Cheap, reversible, and the panel can come off the wall again without destroying the plaster.
• Standoff fixings: holes drilled through the mirror, caps on the face, panel held clear of the wall. Good in bathrooms because air can get behind, good over uneven walls, but every hole is a stress point and a break in the backing, so the holes must be positioned and finished properly.
• French cleats and split battens: the right answer for a very heavy panel or a mirror in a frame. The load goes into timber screwed through to the structure, and the mirror is bonded to a ply back rather than to your wall.
• Full ply or MDF backing sheet, screwed to studs or masonry, mirror bonded to that: what we use in gyms and on any large run. It gives a flat plane, it spreads the load, and it takes the plasterboard out of the argument entirely.

Why bonding a mirror to dot and dab plasterboard is a bad idea

Most new-build flats and a great many refurbished London houses have plasterboard stuck to the masonry on dabs of adhesive, with voids behind. Bond a heavy mirror to that and the adhesive will probably hold. The question is whether the board will. You have created a situation where 30kg is hanging on a 12.5mm sheet of gypsum that is itself only held on by blobs, and the load is trying to peel it off the wall.

When these fail, the mirror does not come away from the board. A patch of plasterboard comes off the wall with the mirror still firmly attached, which is both more expensive and more dangerous. The fix is to find the structure behind, fix a timber or ply backing through the board into the masonry with the fixing packed so you are not crushing the board, then bond to that. A survey takes five minutes and tells us which wall we are dealing with by knocking on it.

Where does a mirror improve a room, and where does it just look like a mirror?

A mirror shows you whatever is opposite it, which sounds obvious and is routinely forgotten. Facing a window it doubles the daylight and gives you a second view of the garden. Facing a blank wall it gives you twice as much blank wall. In a narrow London hallway the mirror wants to go on the long return wall rather than at the far end, because a mirror at the end of a corridor reads as a closed door and a mirror along the side makes the corridor feel twice as wide.

Full height in an alcove is the one placement that nearly always works. A mirror filling a chimney breast recess from skirting to picture rail reads as an opening into another room rather than as an object hung on the wall, because there is no frame and no visible edge to tell your eye it is a surface. The same panel with a 100mm margin of plaster round it reads as a mirror and nothing more.

Where it goes wrong: opposite a cluttered kitchen worktop, where you simply get two bin lids and two kettles. Directly opposite a bedroom door, where you catch movement out of the corner of your eye all evening. And across from a television, which is worse than it sounds. If the only wall available faces something you would rather not look at twice, tinted or antique mirror is a better choice than clear, because it softens the image instead of repeating it sharply.

What is the commonest way people ruin their own mirror?

Cleaning it. Somebody sprays glass cleaner straight at the mirror, the liquid runs down the face, and it collects along the bottom edge where the glass meets the wall. Mirror edges are cut and ground, which means the layered backing is exposed on the arris. Fluid sitting there wicks between the paint and the silver and lifts it, and a year later you have a dark creeping fringe 10mm up from the bottom that no amount of polishing will remove.

Spray the cloth, not the mirror. Wipe, then run a dry cloth along the bottom edge. Avoid anything with ammonia or vinegar in it. In a bathroom, wipe the bottom edge dry after a shower for the same reason. Those three habits are the difference between a mirror that lasts decades and one that is edge-blackened in a couple of years, and they cost nothing.

If you have sizes already, we can price from them. If the recess is out of square, or you are not sure what the wall is made of, our survey across London is free and a written fixed quotation follows it. Call the workshop on 020 4634 6045 between 8am and 5pm, Monday to Friday.