When we talk about glass, the first idea that comes to mind is its breakable nature. At some point, you are forced to cut it. And this is not ordinary glass, but tempered glass. If you don’t know how to go about it, this article is a valuable help. But before getting to the heart of the matter, let’s discover the essentials to consider about this material.
Overview of facts: From my point of view, it is crucial to immediately break a persistent myth: tempered glass cannot be cut once it has undergone its heat treatment. I believe it is my responsibility as an editor to warn you against any DIY attempt that would inevitably result in the panel exploding into a thousand pieces. The only realistic approach is to define its dimensions with absolute precision before manufacturing, because after tempering, the molecular structure of the material no longer tolerates any notch: it’s all or nothing.
What to remember about tempered glass
As its name indicates, it is a glass, but one that has received a specific treatment aimed at optimizing its strength.
Thanks to heating at a high temperature, it is not only hard but also less dangerous. In case of breakage, the pieces may seem less sharp. That is why it can be found almost everywhere, including on smartphone screens. It protects them from shocks and scratches.
This version of safety glass is used in all projects where robustness is sought. Some people use it in the construction of windows, doors, display cases, or shelves.
Others use it in the composition of boat portholes, glass facades, or many other applications. In all cases, it is prized for its high protection and resistance to climatic effects and bending.
I still remember my astonishment during my first bathroom renovation, when I wanted to adjust a shower screen by a few millimeters so that it would fit perfectly under a molding. As soon as the tip of my glass cutter barely touched the surface, a dull cracking sound rang out and the entire pane turned into a mountain of small safety glass cubes. It was a radical realization of the incredible internal tension this material undergoes: a single micro-scratch in the wrong place releases all the stored energy. Since that day, I always measure three times before ordering custom-made: humility in front of glass is a virtue that is quickly learned!
No matter your project, cutting tempered glass is an operation not to be neglected. Here are the steps to follow:
Prepare the equipment
When you intend to cut tempered glass, you must first prepare the necessary tools. Do you also need to drill glass? You must not miss this phase.
Before cutting, put on your protective gear. Wear thick gloves and safety glasses. As for accessories, gather near you a ruler, a marker, a glass cutter, sandpaper, a cleaning product, a tape measure, a brush, and a batten.
Heat the glass then cool it
This technique may be necessary as it undoes the tempering mechanism. It allows the material to become fragile until the cut is easier.
To do this, heat it in a ceramic oven at a temperature around 538 °C for 30 minutes. Then take care to cool it slowly. Try to lower the oven temperature moderately. Then let the glass cool for 2 or 3 hours.
Once this time has elapsed, you can take it out of the oven. If it still feels hot, use tongs to avoid burning your hands. Place the material on a cooling rack for an entire night before cutting it.
Cutting tempered glass
It is necessary to clean the glass surface with a product suitable for windows. Wipe it with a clean cloth. Use your tape measure to take measurements. Draw a line with your marker to serve as a guide for the cut.
Now divide the material in two using a glass cutter. Keep your ruler in place while you score to guide the tool. Press it lightly and follow the line you have drawn. Keep pressing gently to facilitate the cut. Finish the job by smoothing the edges of the tempered glass. You can also read our other article on how to cut tiles?
Comparison of glass types and cutting
| Type of Glass | Cutting Possibility | Recommended Method | Risk in Case of Error |
| Annealed Glass (standard) | Yes | Manual wheel glass cutter | Simple linear crack |
| Laminated Glass | Yes | Cutting both faces + burning the PVB film | Delamination or breakage |
| Tempered Glass (Safety) | No | None (must be cut before tempering) | Complete explosion into small fragments |
| Standard Mirror | Yes | Glazier’s diamond on front face | Silvering chipping |
If you work on classic glazing projects, you might need to learn how to cut a mirror without chipping it. For more malleable materials but requiring precision, mastering the technique to cut plexiglass will be a major asset in your workshop. Finally, in the context of a complete renovation, knowing how to drill standard glass will allow you to securely fix your accessories.
Frequently Asked Questions
No, using a grinder, even with an extra-thin diamond blade, is prohibited on tempered glass. The heat generated and mechanical vibrations would cause the immediate breakage of the internal stresses of the glass. The result would not be a clean cut, but a total disintegration of the panel into safety granules, rendering the object unusable.
Unfortunately, there is no “retouch” solution at home. If the glass is already tempered, you cannot significantly sand the edges nor cut it again. The only solution is to order a piece with the exact dimensions from a glazier or modify the support (wall, rail, or frame) to adapt the opening to the size of the existing glazing.
There are several clues to identify tempered glass. Often, a small indelible logo is engraved in one of the corners (mentioning “Toughened” or “Tempered”). If the logo is absent, you can look at the glass with polarized sunglasses in daylight: you will see dark spots or leopard-like patterns, characteristic of the heat treatment. Additionally, the edges of tempered glass are generally already polished and rounded.
