Thursday 6th October, 2016
They’re both widely used and they’re both known for their reliability and strength, but toughened glass and laminated glass have very different properties to each other. And it’s these differences that dictate when and where each one should be specified.
Laminated glass and toughened glass are both classed as safety glass, so how do you decide which one is appropriate for your project?
Your decision should be based on two factors: WHERE your glass is going to be sited and what the RISK factors are should the glass be broken.
Of course, cost will also have to be factored in to any decision – laminated glass generally comes at a higher premium than toughened glass.
The different properties of laminated glass and toughened glass are established in their differing manufacturing processes. Laminated glass is produced by fusing two or more sheets of plate glass together around a plastic inner layer – generally polyvinyl butryl (PVB) or ethylene-vinyl acetate (EVA).
Should either of the outer layers of glass break, the laminate layer will hold the glass in place, therefore reducing the risk of anyone being injured by loose or falling shards of glass.
Toughened glass is made by putting standard annealed glass through a process of heat treatment called thermal tempering. The glass is heated to around 650°C, just to the point of softening. It is then rapidly cooled. This process puts the outer surface of the glass into a state of compression and the inner surface into tension, which leaves it both physically and thermally stronger.
Toughened glass is generally around five times stronger than plate glass, and can withstand temperatures up to 260°C, as compared to around 120°C for plate glass. Because of its altered state, when toughened glass break, it shatters in its entirety into small glass pebbles.
And it’s this shattering that can be both an advantage and a disadvantage for safety, depending on the circumstances of the application.
For example, glass doors that shatter in this way would be far safer and less likely to cause injury than ones which break into razor-sharp shards. But a glass balustrade that shatters two or more storeys up could well cause injury to anyone who happens to be standing underneath it at the time.
There are also security issues to consider when specifying whether to use laminated glass or toughened glass. For example, it might be thought that toughened glass would be safer for shop windows, but this might not be the right choice for store security – a window that crumbles away to nothing will not provide much of a deterrent to a burglar.
However, on the flip side of this, a laminated glass window in a private residence could prove dangerous should it need to be broken as a means of escape in a fire, for example.
A third option to consider is glass that is both laminated and toughened. This can provide the benefits of both types of glass – glass that is strong yet stays in place when broken.
However, it should be noted that toughened laminated glass also has its own limitations or drawbacks. The primary one being that should the glass be shattered on both sides of the laminate layer, a ‘wet blanket’ effect will result in the glass falling from its frame – which could prove more dangerous than toughened glass alone.
A good alternative to this is heat strengthened laminated glass. Heat strengthened glass is treated to be stronger than annealed glass, but isn’t as strong as toughened glass. It doesn’t crumble in the same way as toughened glass, and heat strengthened laminated glass will remain in its frame when broken.
If you need any further guidance on the type of glass to specify for your project, Tufwell Glass are the experts. Call us or get in touch here, for advice you can trust.