AVOIDING GLASS DELAMINATION
AND ITS ASSOCIATED PROBLEMS
WHAT IS LAMINATED GLASS?
Glass that is being installed into a building has very specific safety standards to adhere to, particularly with respect to glass type, requirements of which vary widely according to the location and purpose of the glass. Windows for example, typically require the use of annealed glass (sometimes called float or sheet glass) but this wouldn’t be appropriate for structural glazing such as balustrade, because annealed glass doesn’t meet the line load requirements for use as a safety barrier. Heat strengthened glass is a fortified version of annealed glass, produced by heating and slowly cooling it – this extra fortification can enable the glass to be used for structural installations, again depending on the line load requirement for the specific purpose. Toughened glass is another fortified version of annealed glass, where increased strength is achieved by heating the glass to an even higher temperature before cooling it rapidly. Toughened glass is typically used for glass door panels and low-level windows as well as some structural glass installations such as balustrade.
Any of these glass types can be sandwiched together to create laminated glass and in respect of balustrade, it is normal practice to bond two panes of toughened glass. The glass is bonded using an interlayer, typically plastic or glue, although there are many main types of interlayer each with its own characteristics. The most common interlayers include PVB (Poly Vinyl Butyral), EVA (Ethyl Vinyl Acetate), SGP (Sentry Glass) and CIP (Cast in Place).
While laminating two sheets of glass together doesn’t necessarily amount to a higher force loading capability (due to movement of the two individual panes of glass under pressure), it is a much safer material to use for balustrade. With laminated glass, in the unlikely event that one pane of glass breaks, the glass shards will largely remain stuck to the interlayer avoiding further damage and potential injury resulting from displaced broken glass. Additionally, in the event of a breakage involving one layer of the laminated glass, there is still a second layer that can serve as a temporary barrier until the pane can be completely replaced.
WHY DOES GLASS DELAMINATE?
Water immersion is the primary cause of glass delamination, so when using laminated glass in an external installation it is important to consider a water drainage solution for the channel. If water is allowed to collect inside the channel, it can begin to seep in between the interlayer and the two glass panels and over time the seepage will grow, causing the layers to separate.
A secondary, but less likely, cause of delamination is the collection of rainwater in the tiny groove at the top of the laminated glass, between the two glass panels and above the interlayer. This only happens if the interlayer doesn’t finish flush with the top of the glass and in a particularly wet environment when the water caught in the groove doesn’t get a change to evaporate naturally.
WHAT ARE THE KNOCK-ON EFFECTS?
Glass delamination usually takes place from the bottom up, since the area affected by water immersion tends to be at the bottom of the glass, inside the channel. The first visible signs of glass delamination is a cloudy opaque quality to the glass, working its way up from the bottom. Opaque glass of course, defeats the purpose of using glass as a material in the first place and the discolouration can look unattractive.
Once the delamination process has started, it escalates rapidly and the glass will need to be replaced, even if the cause of the delamination is addressed. When wind hits laminated glass, it causes the individual panes to vibrate which the interlayer allows for, except when it is perished which can result in the glass panes vibrating against each other causing breakage. And when delaminated glass breaks, there is a greater risk of both panes shattering at the same time.
AVOIDING GLASS DELAMINATION
The key to avoiding glass delamination problems in your exterior glass balustrade installation is to create water drainage points from inside the channel, to prevent water pooling and subsequent glass immersion. Although most channels are fitted with a top bead and/or gasket that lies flush with the glass, these are to prevent debris from getting inside the channel, they are not watertight.
The best place to create drainage points for the channel is at the end of the channel, and there are two ways of doing this depending on whether you are finishing the channel against a fixed feature or not. If the channel ends against a wall or other feature, leave a 2mm gap between the channel and the wall and this will enable water to drain out sideways. Alternatively, if you are fitting an end cap to the channel, drilling a 7mm+ hole into the end cap will provide water drainage. Any smaller than 7mm and you run the risk of the hole ‘self-sealing’ over time. It is also possible to drill drainage holes into the channel itself, one hole every two-metres should create sufficient drainage points to keep the channel clear of water. When drilling into the channel or end cap, it’s important to ensure that the drill holes sit below the bottom of the glass panel, to avoid water immersion.
If your balustrade is in an area prone to water exposure and you wish to protect the top of the glass from delamination, a handrail can be used to protect the top edge of the glass from the elements. For a subtler finish, try using a C-strip handrail. As well as keeping your interlayer dry, handrail creates an extra line of defense in the event of a pane of glass being broken. Find out more about balustrade handrail by clicking here.