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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 types of “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 security 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.
Keep in mind that tempered glass cannot be cut. Once glass has undergone the tempering process, piercing the surface will cause the glass to explode. If using tempered glass for a project, be sure that all sizing is completed before the glass is tempered. In contrast, laminated glass can typically be cut and sized at any time without issue, which could be a benefit for some projects.
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 door or window.
Daniel: So we’re here to break some more glass! What do we have today?
Dustin: So this is an insulated unit. This is essentially what most windows are made up of. It’s two pieces of glass with a spacer in between that creates dead air space, and that’s what insulates it.
Daniel: So this basically what you would find in a residential home for people’s windows?
Dustin: Absolutely. Also in a commercial setting; very similiar process. So this pieces of glass is actually a safety glass. It’s tempered. Both sides are actually tempered. So it takes a really good shot. It’s rigid. But it’s point sensitive, which is why we’ve given you this fun tool to break it with.
So when it breaks- and it doesn’t break like a regular piece of plate glass in big pieces- it breaks into small pieces so if it were to fall on you, obviously it doesn’t hurt you as bad. So why don’t you show us what happens when you break tempered glass.
So what’s really cool about tempered, for me, is that you can typically tell where it breaks from. So it actually spiderwebs from the location. Now, this will continue to crack. It will continue to break.
Daniel: Yeah, we can actually hear it right now.
Dustin: You can hear it, right. And then eventually it will fall out. So tempered glass breaks into these small pieces. Will these cut you? For sure. This can definitely still cut you. It’s still glass. But the reality of it is, this doesn’t cut you as bad, or can cut you as bad, as what the larger pieces do.
So when tempered glass breaks, it breaks into small pieces. We noticed earlier when you hit it, that you kind of bounced off a time or two, right? You didn’t necessarily put much swing into it. Well, tempered is point sensitive because there’s energy trapped inside, but it’s also edge sensitive. So what I want to let you do, is I want you to hit the edge of it. But instead of using a point, I’m going to let you wrench it around and see what you can make happen.
Daniel: Alright, let’s see what happens.
Dustin: Give her a shot!
Daniel: So you can see it’s just kind of like a little chip right there.
Dustin: For sure. Now here’s an interesting piece of this- a lot of times you find or hear of glass breaking spontaneously, right? Spontaneous glass breakage. Something like this can actually cause this piece of glass to break in six months, or in a year. And if that got chipped at some point during the process of making it, and it still got installed, that can explain some crazy day where this piece of glass blows up.
Daniel: And that’s actually really common in the automotive world with sunroofs especially. Those are a lot of times made of tempered glass. People say that they’ll just be driving down the road and all of a sudden the sunroof explodes.
Dustin: Yea, it’s just one of those things that’s really hard to explain and if you try to put a story behind it, there’s really no telling. But that right there can cause an issue for sure down the road.
Daniel: Alright, so let’s take another stab at it…It’s tougher than it looks!
Dustin: Alright, there you go. So with the right amount of force and hitting it at the right angle definitely causes the issue of having it come apart. The other beauty of this is, we didn’t have the back side to hold it in, so you saw that one actually came apart. Similiar story with the sunroof exploding. So there you have it man, that’s kind of how the whole tempering process works.
Daniel: This is laminated glass.
Dustin: This is laminated. So laminated is a type of safety glass. There’s essentially three safety glasses. Tempered, laminated, and then an acrylic or plexiglass, which is kind of a plastic base.
So what we have here is two pieces of glass that are laminated together with a film- an adhesive film. And essentially this is annealed, or plate glass, on both sides.
Daniel: And so where would you find this?
Dustin: So interesting fact: Almost everybody looks through this nearly every day because this is what your windshield is made out of. But also we use this in a lot of areas for storefront. If you see a gas station that has been broken into, sometimes this is what we put in to deter thieves from getting in. It’s a lot harder to get into.
We also use it in bullet-resistant glass. They laminate multiple pieces together. You’ll find it sometimes in residential. And in those cases it’s typically in a hurricane (prone) area where you have to have some blast type of glass.
Daniel: Alright well let’s take a shot at trying to break this and kind of demonstrate what that laminated interlayer does for the glass to keep it together.
Dustin: For sure!
Dustin: So that’s a great first shot. You can see where it broke from. Just like most glass, you can always see where it spiderwebs from and where it goes. That actually looks a lot like what your windshield looks like when a big rock hits it, right? Maybe not quite that extreme. But you can also tell that it’s still intact. This piece of glass’ integrity is there.
Daniel: It’s solid.
Dustin: Correct. I mean, it’s not going anywhere. It also is really not likely to cut you. All of these runs that you see…
Daniel: It’s pretty much totally smooth.
Dustin: It’s smooth! It’s held together by the interlayer. So why don’t you give it a couple more hits in the same spot so we can show just what it takes to literally get through this thing.
So what you can see is the interlayer. You can see the plastic interior of the laminate piece. It actually holds together really really well. So what you’ve done is broken the glass away but the interlayer is still there.
Daniel: Yea, so that’ll deter theft, like you said, in a storefront. If you’re in your automobile and this is your windshield then it’s going to keep your windshield together while you’re going down the road, or god forbid, if you hit the windshield.
Dustin: So a cool piece of this is, all of this damage that you’ve done and this thing is still together. It hasn’t come apart. It won’t hurt you essentially. It could. But for the most part, this is what makes this a safety glass.
Daniel: Yea, and that’s extremely important for residents like in Florida where they have a lot of hurricanes; there’s a lot of wind damage; storm damage. So if this was a window on your home, I think you’d be pretty safe during a hurricane.
Dustin: For sure. You hear about windows blowing out all the time. This would be one of those windows that doesn’t do it.
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