Why Automakers Switched To Glued-On Windshields Instead Of Gaskets

Safety has been a hot topic since the first automobiles began chugging along America's roadways. The first windshields were little more than a standard pane of residential window glass, which protected occupants from things like dust and wind but had a fatal flaw — the potential to separate into large pieces during a collision, threatening severe injury for those in the car. The invention of laminated glass helped reduce injuries from broken windshields, which now crack on impact but don't come apart like modern car side windows that use tempered glass and shatter into glass pebbles.

In the early 1960s, automakers focused on another problem during crashes: keeping cars' occupants from exiting vehicles via the windshield. Windshields' glass kept improving, but the statistics didn't. So the companies started investigating whether the way in which the windshield was installed made a difference. 

Between the 1940s and 1960s, outfits like Fisher Body used a rubber gasket to hold the glass to the vehicle. Some studies found that sticking the windshield to the car with glue was no more or less affective at preventing passenger ejection, though it was less expensive, which was attractive by itself. However, a few decades and advances in adhesive later, "An Evaluation of Windshield Glazing and Installation Methods for Passenger Cars," by the National Highway Traffic Safety Administration, showed that during a crash, the adhesive bonding method reduced by half the number of incidents of both the windshield coming loose and a passenger going through it.

One of the issues with using a gasket to affix a windshield to a vehicle is that it only functions to secure the glass. Modern adhesives, which have been perfected over the years through meticulous chemical engineering, transform the windshield into a structural piece of the car. This isn't easy considering the forces placed on the glass, plus its exposure to debris, precipitation, and temperature fluctuations. But it's important.

For instance, after deploying, many passenger-side airbags wouldn't point at the correct angle without some necessary bracing from the windshield. Without the help of a serious bond, the glass could dislodge, rendering at least one of the front airbags ineffective. This structural function also comes into play if the vehicle flips over, helping the roof maintain its shape even as the vehicle's weight presses down on it. 

According to AmeriPro Auto Glass, a glass-installation company in Jacksonville, Florida, bonded adhesive should withstand 500 to 1,200 pounds of tension per square inch before breaking. However, equally important is a certain level of malleability, which lets the bond between glass and vehicle flex when needed. This is why when getting a replacement windshield, proper curing is essential. You can remove and replace a windshield yourself. However, even after obtaining the specialized tools and materials needed for the job, it can be challenging, and might be better left to professionals.