Even without large cracks through your field of vision, abrasions and small chips will eventually necessitate the replacement of your windshield glass. Despite the solid look and feel, a relatively thin layer of adhesive, not tough metal hardware, actually holds the windshield in place. The strongest adhesives are selected to hold up the windshield's 35 pounds of weight while also withstanding wind, snow and other outside forces. The adhesives are so strong that windshield technicians have to use heat and prying strength to remove the glass during the replacement process. Here are the three main types of adhesive used to secure windshields onto the metal frame of vehicles.

Butyl Rubber Strips

Butyl rubber is a synthetic material that comes in large sticky rolls. Technicians have to press the rubber strips firmly down using the weight of the glass to spread out the bead properly. When expanded, the rubber material creates a solid connection between the vehicle's metal frame and the back of the windshield glass.

In its original state, butyl rubber rolls feel a lot like sticky bubblegum. After curing, the rubber develops a rubber-like feel that does not totally harden. As a result, the rubber allows the windshield to properly respond to vibrations and other minute movements without cracking or breaking. Butyl rubber has a drying and curing time of one hour, making it an obvious choice for mobile jobs or any clients in a hurry to receive their vehicle back.

One Part Urethane

One part urethane is a liquid sealant that does not require any extra mixing. The product arrives ready for instant application. Technicians spread the sealant on each bonding surface and wait for a few minutes to allow the mixture to set up before pressing the windshield in place. As urethane dries, it becomes a clear, slightly flexible connection between the two parts.

The slight material flexibility decreases the likelihood of chips disrupting the cured bond. Since one part urethane is a liquid adhesive, technicians often prefer it for windshield installations against pitted or warped metal frames. The liquid fills in the gaps without reducing the strength of the bond. Cure times are directly influenced by the current temperature and humidity level, so installations using this adhesive are often performed inside a climate-controlled shop.

Scotch Weld Epoxy

The only two part adhesive used for windshield installations is Scotch weld epoxy. Technicians mix together the two ingredients included in the epoxy package to create the adhesive. At that point, it is important to quickly apply the product to the windshield and metal vehicle frame before the ten minute dry time elapses. After the adhesive dries, technicians cannot continue making adjustments to the windshield fitment angle.

The epoxy has a total cure time of one hour, also making it a good candidate for onsite installation jobs performed outdoors. In its liquid form, however, the epoxy is somewhat difficult to apply evenly on the mounting surface within the given time limit. As a result, technicians often leave this glue product for onsite jobs on aged vehicles featuring a windshield mounting surface in poor shape.

Choosing The Right Adhesives

The overall windshield shape and mounting angle directly influences the best type of glue to select for the installation. The different viscosities and drying times play a role in the adhesive selection decision. Corrosive elements, such as rust, can also push the installer to choose one glue product over another.

Of course, technicians have their preferred adhesive products that work for the majority of installations. When a difficult windshield comes along, technicians use their expertise to select an alternate adhesive for the job. Through trial and error, technicians determine the right glue strength and bead size to use for each separate application. Even slight design changes through the model years can alter the way the glue works for the intended installation. 

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