When it comes to mirror, there’s one question that comes up again and again: “How to install it properly?” Unlike monolithic glass, mirror comes with a silvered backing that can complicate installation and handling. We sat down with glass & mirror fabricators and installers, Frederick Robert of Vitrerie Longueuil and Marc-André Deveaux of Vitrerie L.M. , to learn their tricks for a smooth and long-lasting mirror installation. Here are their insights, along with best practices from the National Glass Association and Walker’s own product guidelines.

Mistake #1: Wet mirrors

If mirrors have an ultimate nemesis, it’s moisture. Continued exposure to water will corrode the pretty silver backing right off your mirror, leaving it with all kinds of stain marks and the dreaded “black edge”.  Protect your mirror stock by storing mirror in a dry environment with a stable temperature. Look out for standing water, steam, splashes, and condensation.

When it comes to the actual mirror installation, a dry environment with stable temperature is best. Of course, mirrors are often used in bathrooms, which are prone to humidity and temperature fluctuations. In this case, it’s important to keep the area dry during installation and for 24 hours afterward, or until all glues and sealants have fully cured. When installing a bathroom mirror over a sink, you’ll also want to seal the bottom  with silicone to protect it from splashes.

Mistake #2: Going too big

Regardless of mirror quality, there’s a limit to the size of panels that can be installed successfully and keep their shape. Frederick Robert of Vitrerie Longueuil says that 48” is the widest he’d recommend for mirrors. Beyond that size, you’re asking for torsion and strain on the glass.

When it comes to covering a large wall with a mirror, you may be tempted to use a single large piece. However, it’s better to go with multiple smaller mirrors. Here’s why:

First, interior walls aren’t always perfectly straight. They might have curves or dips that could distort the reflection of a very large mirror. By using smaller mirrors side by side, you can avoid that problem and get a clean, accurate reflection.

Plus, installing a massive mirror can be a real headache. It’s hard to manoeuvre through narrow hallways and doorways, and you risk damaging both the mirror and your walls. Smaller mirrors are much easier to transport and install without any fuss.

So if you’re looking to cover a large wall, consider using multiple mirrors. Deveaux and Robert suggest using polycarbonate setting blocks between sheets of mirror to prevent rubbing and support the mirror on top. Combined with other mounting techniques, these little blocks will keep multiple rows of mirror in place.

Polycarbonate setting blocks can be used as spacers between mirrors. These are available in various widths and colours, right down to 1mm thickness.

Mistake #3: Installing mirror on inappropriate surfaces

First off, mirror is an interior material. Indoor use only, please!

Secondly, you should never install mirror on bare wood, drywall, concrete, brick … you get the picture. Everyone we heard from is adamant about this point, including the NGA. Unfinished surfaces are porous, which means they’re prone to collecting moisture. Do mirrors like moisture? Mirrors do not like moisture. Furthermore, adhesives and other chemical mounting methods won’t bond well to unfinished surfaces, so your mirror installation won’t be secure in the long run. Take the time to seal your wall with a proper coat of primer.

Mistake #4: Rushing the process

We know, we know, waiting for paint to dry is as boring as, well, watching paint dry. But you have to do it. If you rush to mount mirror over a damp coat of primer, you’re trapping that dampness between the mirror and the wall, perfect conditions for the moisture to gradually degrade the mirror’s backing. By now, the very thought of trapping moisture behind a mirror should make you cringe.

The NGA’s whitepaper, Installation Techniques Designed to Prolong the Life of Flat Glass Mirrors, recommends leaving glass mirror installation to the end of a project, and we agree. It’s a great way to ensure that the support wall’s surface is fully cured before you put the mirror in place.

Mistake #5: Using the wrong installation products

There are two main options for mirror installation: mechanical and chemical. An ideal mirror installation will incorporate both methods, but you can get by with just one approach.

Mechanical methods include things like J-moldings, clips and screw, or traditional frames, and they’re sturdier on the whole than chemical adhesives. When you’re using this approach, make sure that your J-moldings have a drainage hole in the bottom (because standing water = death to mirror), and include spacers behind the mirror to accommodate for any variations in the wall. Vitrerie Longueuil and L.M. favour a soft setting tape, which can be twisted for a little extra bounciness.

Setting tape for mirror installation

This sticky setting tape comes in a roll and can be twisted for extra “give”.

If you opt for a chemical mounting technique, you’ll be working with adhesive products like glazing tapes, mirror mastics, silicone, and other specially formulated mirror adhesives. You’ll want to watch out for chemicals that can damage mirror backing, such as acetones, toluols, methylene chloride, and acetic acid. Any corrosive or acidic ingredients are a no-go. Of course, you’ll also want to confirm that the glue is strong enough to hold the mirror’s weight, and that it won’t weaken over time. The safest way to do this is to use products specifically designed for glass mirror installation.

Tips for glues & chemical mounting of mirrors:

  • Apply adhesive in lines of small dots to the back of the mirror, each dot about 10mm across. Larger dollops will dry around the edges while the interior is still soft, which stops the mixture from fully drying out. A damp adhesive is a weak adhesive, not to mention the damage that a permanently damp chemical paste can cause to the back of the mirror. Small dots will dry properly and perform better over time.
  • Create venting “channels” by running your dotted lines of adhesive up and down the back of the mirror, instead of side to side or criss-cross. This way, gasses won’t be trapped between the mirror and the wall, and any heavier- or lighter-than-air fumes will escape out the tops or bottoms of the channels.
  • Caulking gun application is ideal. This lets you apply adhesive without touching the mirror with trowels, putty knives, or other tools that could scratch the back. Cartridges, pails, and drums of adhesives can be paired with powered feed guns, making them even easier to apply.

Acid etched grey mirror at the Macquarium Building, Atlanta.
Designed by Marc Adler
, fabricated by Gardner Glass – Dreamwalls.

Mistake #6: Rough handling

Some building materials can be used, abused, and come out the other side with barely a scratch. Mirrors cannot. To keep these products looking their best, you’ll want to handle them with gloves on. The grit, sweat and oils on human hands are hard on mirror backs, while the mirrors’ cut-glass edges are hard on your hands. Between one thing and another, it’s a mutually beneficial arrangement to keep the gloves on.

Speaking of separation, you’ll want to avoid stacking mirrors right on top of each other or carrying multiple sheets at a time. Fine bits of grit on one piece of mirror can scratch other mirrors, and you’re more likely to drop or bump mirror if you’re trying to handle multiple sheets at once. It may seem like a waste of time to move the sheets one by one, but this will save you time and money in the long run. The same goes for stacking. Piling mirrors on top of one another can lead to scratches, stress and breakage, so you’re better off storing them vertically with spacers between layers.


6mm Bronze mirror at restaurant Marcus, Montreal.
Designed by
Atelier Zébulon Perron, fabricated by Vitrerie L.M.

Mistake #7: Not keeping your business clean

By this point, you know that moisture, dirt and chemicals are hard on mirror. The question is, how do you keep mirror clean without getting it wet? A damp, lint-free cloth with a Ph-neutral detergent is a safe bet. You can also spray glass cleaner onto a soft cloth and use that. Here at Walker Glass, we always keep a stash of detergent-infused sponges handy for photo shoots and trade show displays. Whatever tool you use, you’ll wipe the mirror parallel to the edges to stop water from pooling in joints.

Make sure to clean and dry the mirror thoroughly before and after installation. The NGA recommends leaving glass mirror installation to the very end of a construction project, after most of the mess has been cleaned up. The idea is never to leave dirt, salt, chemicals, or water sitting on the product, especially on the mirror backing.

Setting tape for mirror installation

6mm Starphire Ultra-Clear® mirror with a Satin acid-etched finish at TDC 2, Montreal.
Designed by Huma Design Et Architecture
, fabricated by Laurier Architectural.

Handling mirror can be tricky, but with a little care you can ensure a beautiful, long-lasting mirror installation. Fortunately, experts like Frederick Robert, Marc-André Deveaux and consultants over at the NGA are willing to share their tips and tricks for glass mirror installation.

If you’re ever in doubt, you can always check Walker’s Material Handling page for best practices in installing our mirror and other glass products.

To recap:

  1. Keep your mirror dry.
  2. Cut mirrors to 48” wide or narrower to prevent torsion.
  3. Make sure the support surface is appropriate for mirror: smooth, sealed, and fully cured.
  4. Don’t rush the process.
  5. Use mounting products specially designed for glass mirror installation.
  6. Handle with care.
  7. Keep your business clean.

Now that you’re an expert on mirror installation, it’s time to explore the world of mirrors. Beyond standard clear varieties, acid-etched mirror can improve the lighting in a room by softening and distributing light. Why not add a touch of colour with tints? On the other hand, if you’re looking for absolute purity, a Starphire Ultra-Clear® mirror might be right for you. You can find all the options via these links:

Acid-Etched Mirror

Unetched Mirror

Mirror Samples

About Vitrerie Longueuil

Vitrerie Longueuil, a leader in the glass industry, has been providing unparalleled service and quality for over 50 years. Our reputation is second to none, whether in residential or commercial glazing. Our team has the expertise, know-how and tools to meet the highest industry standards.

Vitrerie Longueuil includes several generations of experts under one roof, yielding a combination of experience and audacity.

Vitrerie Longueuil is your ally for residential and commercial glazing projects.

Learn more at vitrerielongueuil.com

About Vitrerie L.M.

Vitrerie LM is proud to serve the greater Montreal area for over 55 years. We have carved out a place for ourselves in the world of glass as conscientious glaziers, attentive to your needs and offering some of the best turnaround times on the market. We achieve this thanks to our experience, our diversified high-quality inventory, and our state-of-the-art machinery.

Learn more at vitrerielm.com

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