Dear Glass Detective:
I am confused about what type of glass to use to replace the broken glass in the window in my front door. I have been told that it needs to be safety glass and that there are two basic kinds. Can you tell me the difference between laminated glass and tempered glass? Are both of them safe to use?
When selecting safety glass for an application, whether decorative or functional, two choices often arise: tempered or laminated glass. Both qualify as “safety glazing materials” meaning they comply with the current safety glazing codes, so they can be used indoors, in sidelites, railings and other locations which may be deemed hazardous. But tempered glass and laminated glass each have distinct and different advantages.
Tempered glass is made by heating and cooling a piece of standard glass in a tempering furnace. The glass, which must be pre-cut and edged before being put into the tempering furnace, is heated to approximately 1200°F and then cooled rapidly.
This process is also known as quenching. The quenching process leaves the glass hardened so that it is now approximately 4 to 5 times stronger, and therefore more resistant to breakage, then it was before the tempering process. If it does break, tempered glass shatters in small pieces that are less likely to cause injury or damage than non-tempered glass.
Laminated glass is basically a glass sandwich. It is made of two or more plies of glass with a vinyl interlayer between (sandwiched, if you will, as in a car’s windshield). The glass will tend to stay together and case one in is broken – thus qualifying as a safety glazing material.
The other key advantage to laminated glass is that it blocks 99 percent of the UV-light transmission, has sound reduction properties, it can be cut and its edges can be polished after laminating, and lead times are generally faster because most glass shops stock laminated glass. Certain thicker, multilayered forms of laminated glass can even qualify as burglar- and bullet-resistant glass.
Because laminated glass holds up to impact better than other types of glass, this is what is used in modern windshields. The sandwiched interlayer gives the glass structural integrity and keeps it from shattering apart like tempered glass might. This is key for effective airbag deployment and helping to keep occupants inside the vehicle in the event of a crash.
This intact breakage illustrates how tempered glass forms tiny, countless pieces. However, most tempered glass shatters to the ground upon impact.
Note that even though there was a powerful impact, this tempered glass has remained structurally intact.
So for strength and breakage-resistance, temper glasses often is the first consideration. For flexibility, UV-resistance, security and sound considerations, laminated glass is often the product of choice. Both are considered safety glazing materials and can be obtained in a variety of thicknesses and colors or tints. Both are easy to clean and maintain when installed properly.
Typically, laminated glass products are a slightly higher price than tempered products of the same type and thickness. The optical clarity for both laminated and tempered glass are excellent in either product will provide many years of satisfactory service in your front door.
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