Volume 33, Number 3, March 1998


Combo Deal

Mirror Installations with Adhesive and Mechanical Fasteners

by Robert Cline

If you are selling adhesives to install mirrors, why do you suggest the use of mechanical fasteners? This is a question our customers ask several times a week. After 20 years of involvement in the construction industry as a laborer, supervisor, rep or manufacturer, I have made several observations that support the combined use of adhesives and mechanical fasteners when installing mirrors.

For most installations, an approved and tested mirror mastic will hold a mirror without any type of mechanical support system after having ample time to set-up. Each adhesive manufacturer has instructions on its product explaining how to do this. However, there are so many variables involved in installing mirrors that I advise the use of some type of mechanical support system.

As adhesive products are developed to meet new needs, requirements or federal specs, the installers need to stay up-to-date. The best way to do this is to follow the directions on the manufacturer’s containers or literature.

Substrates are the crucial link in mirror installations. In general, the adhesive used will be stronger than the wall material upon which it is used. All porous substrates such as plywood, drywall, plaster, concrete and cement block should always be sealed. A sealer adds strengths to the wall and prevents caustic chemicals found in these products from attacking the mastic or the back of the mirror. Products like chipboard or particle board sometimes have a wax fused to the surface when manufactured. Be sure to sand these surfaces before applying a sealer.

Fire-retardant plywood and other treated lumber is not recommended as a substrate when installing mirrors. Chemicals in the wood will cause a loss of adhesion over time. Wallpaper is a common substrate found in most homes. Wallpaper does not provide a strong surface for a mirror application. Cut six-inch diameter holes in the wallpaper or completely remove it, then apply mastic to the re-sealed wall.

Paint is a major area of concern. Several paints on the market, for one reason or another, do not have the properties that provide a quality installation. A low-cost, "high-hiding" paint may contain ingredients that make them chalky when dry. Before installing mirrors over paint make sure it’s dry and that it won’t leave a powdery residue on your hands as you rub the walls. If you have any question as to the paint being strong enough to hold, sand wherever you plan to apply mastic. Clean the area and seal according to the manufacturer’s instructions. Mirror clips are a good back-up system for your mastic if you have any reservation about painted surfaces.

Always take time to check for dampness, unsealed surfaces, loose plaster, dust and poor-quality paint. Never install mirrors on freshly painted or plastered walls. Give the wall time to cure and follow the manufacturer’s instructions.

Another important issue when installing mirrors is movement. All buildings tend to move no matter what the age of the structure. Mirror mastics are designed to stay flexible and soft when they dry. This helps to avoid most of the problems associated with structural movements. Some of the newer adhesives, which are very flexible, have been designed to be used in gyms, health clubs, high-traffic areas and other places where movement might be a problem. The use of trim, clips and setting blocks provide insurance against mirror failures due to movement.

Fitting mirrors too tightly can be a real problem. When mirrors are set too close together or set too tightly to the wall, stress can occur. This can cause mirrors to crack or pop lose. The mastic can also be applied so thin that it loses some of its flexibility and adhesive properties. Mirrors should always set away from the wall so that any moisture that might get behind the mirror can evaporate. The use of J-channel with mastic will allow for these clearances.

With all of the above situations and variables, it makes sense to use only approved and tested mirror mastics along with a strong mechanical support system. Don’t let common sense be overcome by cosmetics. By using both adhesive and mechanical fasteners you are providing your customers with a professional, safe, durable installation that will stand the test of time.


Robert (Bob) Cline is national sales manager of Gunther Mirror Mastics, a division of Uniroyal Adhesives and Sealants, South Bend, IN. He has more than 17 years of experience in the adhesive and sealant industry.


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