One Balcony Panel Exploded, Two Had to Be Replaced

A balustrade panel on this balcony let go on its own. Nobody hit it, nothing fell on it. One moment it was a sheet of glass and the next it was a pile of blue green pebbles across the deck, with a good share of it gone over the edge into the garden bed below.

The panel beside it stayed standing, but it did not come through unscathed. The break chipped its edge, and a chipped edge on toughened glass is not a cosmetic problem. What started as one broken panel became two.

Toughened glass really does break on its own

This is the part people find hard to believe, and we understand why. Balustrade glass is toughened, and toughened glass is the strong stuff. It should not fall apart while everyone is inside having dinner.

But toughened glass is under enormous internal tension by design. That is what makes it strong, and it is also what makes it fail the way it does, all at once and into small blunt pieces rather than long blades. If there is a tiny impurity trapped in the glass from manufacture, it can very slowly grow over years until the tension has nowhere to go. Edge damage and pressure on the glass can do the same thing.

When it finally goes, it goes completely, and there is rarely any warning. The blunt pebbles are the safety part working exactly as intended. It is still a mess, and on a balcony it is a mess that lands in two places at once.

One panel broke, two needed replacing

Glass that lets go with that much stored energy does not do it quietly. The panel next to it survived the event, but the edge took a hit and chipped.

What that leaves behind is what we call a slither. A thin feathered spike of glass running along the edge, and it is about as sharp as glass gets. That is not something you want at hand height on a balcony, on a run that people lean on and children put their hands on.

It is a structural problem as much as a safety one. As above, edge damage is one of the things that sets toughened glass up to fail later. A chip is a stress concentration sitting in a panel that is already under tension, so leaving it there is really just waiting for the second one to go.

So both panels were measured for replacement.

That is worth knowing if it happens to you. The panel you can see in pieces is not always the whole job, and it is better to find that out at the measure than on install day.

Concreted in, not channelled

Modern frameless balustrades sit in an aluminium base channel. The glass is packed, aligned and wedged in place, and if a panel ever needs to come out it can be unwedged and lifted.

This balcony predates that. The panels were set directly into a slot cast into the concrete, then grouted solid. It is a perfectly sound way to build a balustrade and there are thousands of them around Geelong and the coast. It just means a broken panel cannot simply be lifted out.

Getting the old glass out

The remains of both panels were still locked in the slot, so they had to be broken out. That is jackhammer work, done carefully, because the concrete either side of the slot is the thing holding the whole balustrade up and the neighbouring panels are still live glass sitting a few centimetres away.

Once the old glass and grout were out, the slot was chased back to clean concrete, then swept and vacuumed. Any grit left in the bottom of that slot becomes a hard point under the new glass, and a hard point under the glass is how you end up doing this job twice.

Setting the new panels

The replacements came back as toughened safety glass, made to the sizes taken off the opening.

Each panel was lowered into the slot onto packers. The packers do two jobs. They set the finished height so the tops line through with the existing panels, and they keep the bottom edge of the glass off the raw concrete. Glass sitting hard on concrete is glass with a stress point on it, and that is the beginning of the next breakage.

With the panels sitting at the right height, timbers were screwed off to hold them plumb and in line with the panels either side while everything was set. On a balustrade the eye picks up a panel that leans or steps out of line long before it notices anything else.

The bit that matters most, the grout

The slot was filled with non shrink construction grout. Not concrete, not sand and cement, not whatever is left in the shed.

Ordinary cement based mixes move. They shrink as they cure and they expand and contract with heat and moisture afterwards. Around a fixed pane of glass that movement has to go somewhere, and where it goes is into the edge of the glass. You end up with a panel being squeezed by the very thing that is meant to be holding it.

Given that this glass had already broken once from internal stress, the last thing anyone wants is a mount that adds more of it. Non shrink grout holds its volume as it cures, so the panel is held firmly without being clamped, and it stays that way through summer and winter.

It costs more than a bag of general purpose cement. It is not the place to save the difference.

Seven days braced, then finished

The timbers stay on for seven days. Non shrink grout needs that long to come up to full strength, and until it has, the panels are held plumb and in line rather than trusted to stand on their own.

That is worth saying out loud to anyone waiting on a balustrade repair. The glass goes in and the job looks all but done, but it is not finished until the grout has reached strength and the bracing comes off. Rushing that is how a panel ends up a few millimetres out of line with the run, or worse, not properly held at all.

At seven days the timbers come off and the balustrade is back to a continuous run of glass with the view through it unbroken.

If a balustrade panel has gone at your place

Two things are worth doing straight away. Keep people away from underneath it, because glass that has dropped off a balcony is rarely all on the deck. And do not lean on the panels either side until someone has looked at them, since a neighbouring panel can be damaged without it being obvious.

Send us a photo of the balustrade and the run it sits in, and let us know whether the glass is set into a channel or grouted into the concrete. That one detail changes the job, the price and how long it takes.