Dark Graphics Cracked This Bank Window, Then Held It Together

The shopfront window at the NAB branch in Geelong West had a crack running through it. Nothing had hit it. The glass had cracked itself, and the dark logo graphics applied to the front of it were the reason.

How dark graphics crack a window

Glass cracks thermally when one part of a pane is much hotter than another part. The warm section expands, the cooler section will not let it, and the stress has to go somewhere. It goes into the glass.

Dark signage graphics are particularly good at causing this, and it is worse than an even tint across the whole pane. A logo covers some of the glass and leaves the rest clear. The covered area absorbs sunlight and climbs in temperature, while the clear glass beside it stays comparatively cool. Now you have a hot patch and a cool patch in the same sheet, centimetres apart, pulling against each other.

Add the edges, which sit shaded inside the frame and stay cooler again, and there is a lot of tension in a pane that is simply standing there in the sun.

You can usually pick a thermal crack by its shape. It starts at the edge, runs square out from it for a short distance, then wanders across the glass in a slow curve. No impact point, no star pattern, nothing to explain it. Just a line that turned up on its own.

The glass underneath was float

This is where it stopped being an inconvenience and started being a hazard.

The original pane was float glass, also called annealed. Ordinary glass. It has the lowest resistance to thermal stress of anything we fit, which is what let it crack in the first place, and it breaks into large sharp pieces rather than crumbling or holding together.

A cracked sheet of float glass, at full shopfront size, standing over a public footpath outside a bank. That is not something to leave sitting for long.

The graphics were the only thing holding it in

Here is the part worth pausing on. The graphics that caused the crack were also the only reason the glass was still in the frame.

That dark vinyl had effectively become one enormous sticker laid across a broken pane, holding the pieces to one another. Peel it, knock it, or let the wind get behind it, and a cracked sheet of float glass comes out in shards at head height on a public path.

Out in pieces, on purpose

A pane in that condition does not come out in one piece, and trying to make it is how people get hurt. It was cut out and taken down section by section, the graphics peeled back progressively so the glass was released a bit at a time instead of all at once.

Slower than lifting a whole sheet out. Considerably better than the alternative on a footpath outside a bank in the middle of the morning.

The whole frontage was shut off first

Before a single piece of glass moved, the entire section of shopfront was barricaded. Hazard tape strung between the bollards, the truck positioned to close off the approach, and a clear exclusion zone with nobody inside it who did not need to be.

This is a bank on a busy strip. There are people walking past on the footpath, cars pulling into the parking bays right in front of the window, and customers heading for the door. Every other risk on this job could be managed by how we worked. The public walking underneath a sheet of cracked float glass was the one that could not, so it gets removed before anything starts.

It is the least interesting photograph of the day and probably the most important one.

Laminated safety glass going back in

The replacement is laminated safety glass, which is what current standards require in a shopfront like this one. Older buildings are full of float glass in positions that would never be approved today, and a replacement is the moment that gets corrected.

Laminated is two sheets of glass bonded to a plastic interlayer. Break it and the interlayer holds the pieces in place, so it does not empty itself onto the footpath. In other words, the thing the graphics were accidentally doing on the old pane is now built into the glass itself, by design.

If you want the difference between float, toughened and laminated set out plainly, we cover it on our glass types page.

Why it is clear glass in the photo

The branding for this window is being reapplied separately by others, at a later date. There is a wall built directly behind the glass that cannot be moved, which changes how and when that work can be done.

So the panel goes in clear and correct, and the graphics follow when it suits the people doing them. That is normal on commercial jobs. The part that could not wait was the broken glass over the footpath.

Putting graphics on a shopfront? Ask what the glass is first

Signage is not the villain here. Dark signage on the wrong glass is.

If the pane is old float glass, a large dark graphic is a real risk rather than a theoretical one, and replacing the window afterwards costs far more than asking the question beforehand. If the glass is toughened or laminated it handles the heat far better, and in most cases the graphics are perfectly fine.

Either way it is worth a two minute conversation with whoever is fitting the signage, or with us, before a full colour logo goes across a shopfront that has been standing there since the eighties.

We do this kind of work across Geelong regularly. We recently replaced a 200 kg shopfront panel at a Commonwealth Bank branch, a very different problem with the same requirement, which is that the footpath stays open and nobody gets hurt.