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Some glass is exposed to direct sunlight for long periods of time. Some is coated with a substrate, like silicon, that makes long-term adhesion difficult to achieve. And some is topped with anti-reflection or scratch resistance films that make removing the graphic without damaging the tint nearly impossible.

Likewise, all vinyl is not created equal. Windows require cast instead of calendered film, for example. More specifically, perforated films designed for flat, transparent surfaces are ideal for glass applications. This cast vinyl has a continuous hole pattern perforated into the film to provide a graphic visible from the outside that can be seen through from the inside.

Keep in mind that many different factors influence the performance life of window graphics, including the correct combination of film, ink, overlaminate, ink formulation, drying methods, exposure conditions, and cleaning methods and maintenance. In this article, we will discuss the preparation of the substrate and application methods.

Preventing Problems
There are several pre-application steps you can take to prevent potential problems during and after installation. One of the most basic tips is to use an overlaminate or clear coat for durability. This will protect the film from environmental factors like dust, water and dirt that can collect in the perforated areas.

One thing you cannot accommodate for is sunlight. For that reason, you should steer clear of using dark graphics and vinyls on window fronts, according to Jeff Stadelman, technical marketing manager for the graphics product group at MACtac, a manufacturer of pressure sensitive adhesive. “If you cover window fronts with dark vinyl, then the vinyl will absorb more heat. It will also hinder the ability of the glass to give that heat off,” he says. “Eventually, the glass could actually explode because of the prolonged intensity of the heat.”

Cold weather also plays a role in vinyl application to glass. Manufacturers do not recommend attempting to apply vinyl to glass when the air surface temperature is less than 40 degrees Fahrenheit because the adhesion will not stick. (For more information about how environmental conditions impact vinyl application, read “Considering Environmental Conditions.”)

Preparing for Installation
Now that you have skirted some potentially troubling issues, it is time to prepare the glass for application. This means a thorough cleaning.

“Some people tend to use ammonia-based cleaners to clean glass, but that leaves a film on the window and can affect adhesive on the film,” says Oracal product specialist Lindsay Howard. “It can cause bubbles, which is a sign of outgassing, or the life of the adhesion may be shortened. It is best to use isopropyl alcohol instead.”

Before you begin applying the vinyl it is important to size the window. The idea is to cut the film to the approximate shape of the window before squeegeeing it. Avery advises to measure the decal to make sure the graphic fits in the window with a clearance around any rubber gasket. At no time should the graphic touch or overlay any window moldings or you could lose adhesion.

If you are applying a graphic that will bridge painted metal surfaces between windows, 3M offers some good advice: apply an opaque film to the surfaces between the windows before applying the window graphic and you will eliminate any inconsistencies in the vinyl.

Applying the Vinyl
Manufacturers do not recommend wet applications for perforated film graphics because water will get trapped in the holes and cause the vision to be obscured when you look through the graphics. Dry applications is the only warrantied method. (For more information on how to apply dry, read “Boosting Vinyl Adhesion in Dry Applications.”)

The first step to successful applications is to tack down the film in the center of the window and cut the graphic to shape. 3M recommends flipping the graphic up using the low tack tape (masking tape) as a hinge and then start removing the liner from the graphic. If you apply the graphic and then cut away a margin of 1/8 inch to 1/4 inch, then you will eliminate the need for edge sealing on full window coverage.

The next step is to flip the graphic back down and start applying pressure on the film to create adhesive contact to the window, removing the liner as you go. Experts recommend using a low-friction sleeve on the plastic applicator of the squeegee to prevent scratching the graphic.

Now, start a squeegee action in the middle of the image and squeegee from one side to the other, continuing the process from the top of the decal down using overlapping strokes and removing the liner as you go. If needed, Avery recommends carefully adjusting the graphic to realign the material or take out wrinkles. Resqueegeeing should always follow this action.

If you encounter two panels designed to meet side by side on a window, 3M has some good advice. The manufacturer recommends carefully trimming the images so that the panels meet and form a butt seam. But do not overlap panels and always trim before starting the application. If you cut the film while it is on the window, then you may permanently scratch the glass.

If there are any edges and seams, then you’ll have to use an edge sealer to prevent water and contaminants from getting under the film and obstructing the interior view or contaminating the adhesive, according to Avery. The sealer should be applied carefully to completely seal the edges and also minimize the distortion caused by sealer from the viewing side of the graphic. Using a 1/4-inch brush to apply sealer gives you greater control and makes it neater.

Removing the Vinyl
Manufacturers also have specific recommendations for removing the vinyl without damaging the glass. There are two methods: heat and chemical.

The heat method employs a heat gun, lamp or propane torch. Begin by heating one corner of the marking, using caution to prevent the material or window from getting too hot, which could cause the glass to shatter. Then, Avery recommends using a razor blade or knife under the corner to loosen the marking, being cautious not to damage the glass. Next, grasp the lifted edge up and pull it up and away from the glass with a slow even rate at an angle less than 90 degrees. Always keep even pressure and heat the area of film immediately ahead of the area being removed.

If the film has been clear coated, then you can use the chemical removal system, but experts say this process is not as effective on overlaminated materials. Vinyl film manufacturers recommend following instructions of the chemical suppliers.

Vinyl manufacturers recommend using Xylol (Xylene) if adhesive or edge sealer remains after the film is removed. Let the Xylol soak into the adhesive or edge sealer, then use a plastic squeegee to scrape off the residue. You can repeat this process as necessary until the glass is clean. Non-flammable citrus-based removers are also ideal for this task.

Always check with the vinyl manufacturer before applying the film to glass. Some do not recommend, and usually will not warranty, applications to surfaces other than vertical windows, to windows that have built-in heating, to windows with defrosting elements or wipers, to substrates with special coatings, to regulated vehicle windows, to windows that crank or roll down, or to emergency window exits.