FABRICATING DEBRIS

While different areas of the country have different rules about where tempered glass must be used, the general rule of thumb is that if someone could stumble and fall into glass, the glass is required to be tempered. For example, glass doors are made of tempered glass. Most states require that glass placed within about 18 inches to the floor must be tempered. Stairwells that use glass on the sides usually must be tempered. And so on.

There are a couple of common misconceptions about tempered glass. First, tempered glass is not softer than annealed glass; both have the same hardness. Second, tempered glass has the same surface quality or smoothness as annealed glass. It is not rougher. However, some tempered glass has a poor-quality surface due to fabricating debris, which can cause it to scratch when cleaned. If you are using the same equipment and same procedures when cleaning tempered glass and annealed glass, yet you are only scratching tempered glass, it’s likely due to the poor surface quality of the tempered glass, not your cleaning techniques.

Because tempered glass is designed to shatter into tiny pieces, it cannot be cut after it’s fabricated. That means it is always cut to the size of the finished product before it’s tempered. Once the glass is cut, the fabricator takes a belt seamer or diamond grinder to grind down the edges. Next, the glass is run through a glass washer. After being washed, it goes into an 1150 F degree tempering furnace. When it comes out of the furnace, it is quenched on both sides with cold air. This process creates the temper by forming a compression layer on both sides of the glass and a tension layer in the middle the glass.

Some glass manufacturers produce tempered glass with no problems, while others produce tempered glass that frequently scratches. This means that fabricating debris is a quality control issue on the glass fabricator’s part.

The problem occurs when some fabricators do not clean or maintain their equipment. The glass washer seems to be the most common problem. After the belt seamer or grinder is used on the glass, it creates a lot of glass dust or “debris” on both sides of the glass. The glass washer is designed to wash that debris off, but if the glass washer is not maintained correctly – such as not being emptied out regularly or not having filters changed often enough – then the glass is not washed thoroughly. If debris is left on the glass when it enters the tempering furnace, those fine particles fuse onto the glass surface. The debris becomes a permanent part of the glass itself that won’t simply wash off. Then later, when the window cleaner scrapes the glass, it removes the defect and causes scratched glass.

If tempered glass scratches, it usually occurs on the bottom surface of the glass. That’s because if glass becomes contaminated with debris by an improperly working glass washer, that contaminated glass can also leave debris on the rollers. So even if the washer problem is fixed, the rollers may still be affected and cause defects.

To figure out which side of the glass is the bottom side, look for the glass stamp. Most tempered glass stamps are either sandblasted or porcelain. Sandblasted stamps are always placed on the bottom of the glass. You can tell if the stamp is sandblasted if you don’t feel anything when you run a razor blade across it. (You may hear it just a little bit.) Porcelain stamps are always put on the top of the glass because the rollers would smear the stamp if it was placed on the bottom. Knowing what type of stamp is used will help you identify which side of the glass is possibly defective.
Heat Treated Glass, which is often used in commercial buildings, goes through a process similar to tempered glass. With heat treated glass, once it comes out of the furnace the glass is blasted with cold air, which causes it to cool quickly. This makes it about twice as strong as annealed glass, but not as strong as tempered, and it breaks more like regular annealed glass.

Like tempered glass, fabricating debris can cause problems with heat treated glass for the same reasons. However, it can be harder to identify the problem side of the glass because heat treated glass does not have a stamp like tempered does.

Low-E Coatings are growing in popularity in today’s insulated glass (IG) markets. Low-e coatings are designed to minimize the amount of infrared light allowed through the glass without compromising the amount of visible light transmitted. Low-e glass has a microscopically thin transparent coating that reflects heat. So, when it’s cold outside and the building’s heat tries to escape, low-e coatings reflect the heat back inside. The reverse holds true when it’s hot outside.

Years ago, the low-e coating was added after the tempering process. These days, however, a lot of manufacturers add the coating before the tempering process. When added before tempering, the coating cannot be face down in the furnace. This is another way to tell which side of the glass is the roller or bottom side. The coating will be facing the top, which means the side with fabricating debris is on the opposite side.

Low-e coatings in warmer climates should be on the inside glass, and scratches will be on the outside glass. In colder climates, the low-e coating will face the outside with scratches on the inside.

Any time you work with these types of glass – as well as any time you are cleaning new construction or needing to use a razor – you need to have your customer sign a waiver that says you are not responsible for scratches caused on the glass. Download a free sample of a scratched glass waiver here. Additionally, do not sign anything that says it is your responsibility to point out fabricating debris on the glass.

If you ever do accidently scratch a window, there are professional options available that can remedy the situation. Our friends at GlassRenu have made it easy. When it comes to glass care and maintenance, GlassRenu is the authority. GlassRenu first introduced their line of glass restoration tools years ago, starting with the Contractor Grade Scratch Removal System. It’s perfect for removing scratches from glass but it also helps with hard water stains, building run-off, construction clean up, pet scratches, scratch tag graffiti. It even removes scratches caused by fabricating debris. It’s also a great way to earn more money on the job. Scratch Removal itself is a great add-on service. Now with professional-grade systems available on the market, it makes a lot of sense to own one. Consider it an on-site insurance policy if you accidentally scratch some window on the job. Check out the Glass Renu Scratch Removal kits here.

It is also smart to carry “Care, Custody and Control” insurance. General liability insurance does not cover damage that was done to the actual surface you are cleaning, including scratched glass. Only Care, Custody, and Control coverage does that.