To understand fabricating debris, you need to understand how why and how tempered glass is made.
What Is Tempered Glass
Tempered is designed with safety in mind, as it’s up to five times stronger than untempered (i.e., annealed) glass. It’s harder to break tempered glass, and when it does break, it shatters into tiny pieces.
In general, tempered glass must be used in locations where a person could stumble into the glass and break it. In most parts of the country, glass doors, glass stairwells, and glass placed within about 1.5 feet from the floor must be tempered.
How Tempered Glass Is Made
Tempered glass starts out being made the same way as annealed glass, but then goes through a different cooking process.
Tempered glass is always cut to size before it’s made since it would shatter if cut afterwards. The glass fabricator takes the piece of cut-to-size glass and grinds the edges down using either a belt seamer or diamond grinder. Next, the glass runs through a washer, then is placed into a 1150-degree tempering furnace where it’s reheated. Finally, the hot piece of glass is blasted with cold air on both sides. This is what creates the temper. The blast of cold air produces a compression layer on the inside and outside of the piece of glass, while the middle has a tension layer.
Fabricating Debris on Tempered Glass
Some brands of tempered glass can be cleaned with no problems, while other brands of tempered glass tend to scratch a lot. This happens because some glass fabricators do not keep their glass-making washers as well cleaned or maintained as others, which leads to scratching.
As I already mentioned, the edges of tempered glass are hit with a grinder. This creates a lot glass dust, which needs to be cleaned off – i.e., the glass washer’s job. However, if the washer or rollers are not also regularly cleaned, that microscopic dust stays in the washer and can make its way onto other pieces of glass as they go through the washer. Once the glass hits the furnace, those tiny dust particles are fused onto the glass, and the debris has now become one with the glass. When a window cleaner later comes along and scrapes the glass, it removes the dust – which is now actually a part of the glass – and scratches can occur.
How to Find the Bottom Side of Tempered Glass
Glass usually only has fabricating debris on one side – the bottom side – because it’s the side that hits the rollers when going through the manufacturing process. This is the side that may scratch.
Tempered glass manufacturers must mark it with a stamp that usually says either “tempered” or temp” in one or more of the corners. If you find a sandblasted stamp – i.e., one that you can’t feel if you run a razor across it – it’s on the bottom of the glass. If you find a porcelain stamp – one you can feel – it will be on the top of the glass since the porcelain would smear if it ran across the rollers
Heat Treated Glass
Commonly found in commercial buildings, heat-treated glass is stronger than annealed glass, but not as strong as tempered glass. It goes through a similar manufacturing process as tempered glass, and can attract fabricating debris as well.
Like tempered glass, heat-treated glass can pick up fabrication debris, which can lead to scratches. Heat-treated glass does not have a stamp, however, so it’s harder to determine which side of the glass is the bottom side, i.e., the side that’s more likely to scratch.
Low-e coatings are popular on tempered glass to help create insulation. The coatings are designed to reduce infrared light levels without decreasing the amount of visible light let in by the glass. Low-e works by using an extremely thin coating that reflects heat, making it harder for a building’s cold air to escape in the summer, or heat to escape in the winter.
With today’s technology, low-e coatings are usually applied before the glass is tempered. The coating is added to the top layer of glass because is cannot be face down in the furnace. This means that the opposite side (i.e., the bottom) is the side that is more likely to scratch due to fabricating debris.
When trying to figure out which side of low-e glass may scratch, think of it this way. In warm climates, the low-e coating is usually on the inside glass, which means the outside glass is the one that may scratch. In colder climates, the coating is on the outside and the inside of the glass may scratch.
The ETEKT Low-E coating detector can also make it easy to detect Low-E coatings on double pane windows from a single side.
How to Protect Yourself
- Have your customer sign a waiver saying you are not responsible for scratches caused during cleaning. You can find sample waivers here: