A Vandalised Toughened Panel at Norlane, Concreted Back In

A toughened glass panel at a site in Norlane was vandalised, and toughened glass that is hit hard enough does not crack. It explodes. The whole sheet lets go at once into thousands of small pieces, and what is left behind is an empty channel full of broken glass.

This panel was not screwed into a frame or clamped at the base. It was concreted into a glazing channel, which is how a lot of balustrade and barrier glass gets installed on commercial sites. It looks clean because there is no hardware showing, and it is strong because the whole bottom edge of the glass is locked into the slab. It also makes the replacement a very different job to swapping a window.

Breaking out the old panel

There is no way to lift the broken glass out of a channel like this, because the bottom hundred millimetres or so of the sheet is set into hardened material. The only way back out is to break it out.

That is a jackhammer, a channel full of shattered toughened glass, and rain coming down the whole time. It is slow, loud work, and it has to be done carefully. Go too hard and you damage the channel itself, and then the job turns into a concreting repair before it can be a glazing job at all.

Cleaning the channel out

Once the glass and the old material are out, the channel has to be cleaned back to bare, sound sides. Every bit of grit, old packing and glass dust has to come out of it.

This step decides whether the finished job lasts. The new panel is only as good as what it is set into, and anything left in the bottom of that channel becomes a hard point under the glass. A hard point under a sheet of toughened glass is exactly what causes the next failure, months later, with nobody standing anywhere near it.

Standing the new panel up and holding the line

The new panel gets lowered into the channel and then propped with timber supports before anything is poured around it. The timber does two jobs. It holds the glass plumb, and it holds it in line with the panels either side of it.

That second part matters more than people expect. A run of balustrade glass is read as one straight line from a distance. If one panel sits two or three millimetres proud of its neighbours, or leans a fraction out of plumb, your eye picks it immediately, and nothing can be done about it once the channel is set.

Why we use a structural non-shrink mortar, not concrete

The panel is fixed in place with a specialist rapid set structural non-shrink mortar. That is not the same thing as concrete, and the difference is the whole reason the job holds up.

Ordinary concrete and standard rapid set products move as they cure. They shrink, and some expand before they shrink. Either way, that movement happens hard up against the edge of a sheet of glass held tight in a narrow channel, and glass has nowhere to go. The pressure builds at the edge, which is the most vulnerable part of a toughened panel, and the result is a panel that fails weeks or months after it was installed, for no obvious reason.

A structural non-shrink mortar is engineered to cure without that movement, while still reaching the strength needed to hold a barrier panel. It costs more and it is less forgiving to work with, and it is the correct material for glass set into a channel.

It is also messy and it goes off fast, so the pour is the part of the day where nobody stands still. Mix, pour, work it into the channel, check the panel is still plumb and still in line, clean the faces of the glass before anything cures on them. Then it is done, and the propping stays until it has set.

The finished run

New panel in and set, with the channel finished off level with the rest of the run.

From the front, there is nothing to pick. That is the point of a concreted-in panel, and the reason it is worth doing properly rather than converting it to a clamped or framed fixing to save a day.

From the side is where the line shows. The new panel sits flush with the panels either side of it, which is what all that timber propping was for.

If a panel on your site has been vandalised

Keep people away from the opening first. Toughened glass that has let go leaves loose pieces in the channel and along the ground, and a barrier with a panel missing is a fall risk until something is put across it.

Send us a photo of the whole run, standing back far enough to get the panels either side of the broken one, plus your suburb. On a job like this the photo tells us the panel size, the fixing type and the access, which is most of the quote. We can make the opening safe the same day and come back with the new panel once it is toughened to size.

If it is going through insurance, we deal with insurers and builders directly, and there is more on how that works on our insurance glazing page. We have written up another concreted-in job on a balcony balustrade panel, and there is more on panel types and thicknesses on our glass types page.