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FREQUENTLY ASKED QUESTIONS
This section contains answers to some frequently asked questions. To skip directly to a certain section of the page, select the category from below.
Scratched Glass and Scratch Removal
Construction Window Cleaning
Insulated Glass Units (IG Units)
Low-E Coatings
Heat Treated Glass
Scratched Glass and Scratch Removal
Q. What are the most common causes of scratched glass?
A. Workers putting tools on windows, plasterers wiping plaster off glass, painters and texture crews dry scraping glass, untrained window cleaners removing construction debris from glass, and defective tempered glass can all result in scratched glass.
Q. Do metal scrapers or razor blades scratch glass.
A. No. Metal scrapers and razor blades alone will not scratch glass. However, abrasive materials, such as sand or fabricating debris from the tempering process, trapped by a metal scraper or razor blade, can scratch glass.
Q. Can scratches be taken out of glass? Does it matter if it is tempered?
A. Yes. Most single scratches can be removed from glass. It's very difficult to remove scratches over the entire surface of defective tempered glass. If attempted, glass distortion may result.
Q. Can chips be removed from glass?
A. Yes, but we do not recommend that practice. Removing chips requires the removal of significant amounts of glass and often results in severe glass distortion.
Q. How deep of a scratch can be removed from glass?
A. A scratch you can catch your finger nail in can usually be removed. Scratches much deeper than this might result in glass distortion.
Q. Can acid graffiti be removed from glass?
A. Yes. With the proper equipment, most acid graffiti can be easily removed from glass without any destoration.
Construction Window Cleaning
Q. What is construction window cleaning?
A. This type of window cleaning requires the window cleaner to be specifically trained to remove several types of construction debris from the glass without scratching.
Q. What are the most common tools used to remove construction debris from glass?
A. Metal scrapers and razor blades have been the standard for construction window cleaning and remain the proven method to safely remove construction debris from glass without scratching.
Q. What chemicals are used to remove plaster, concrete and mortar from glass?
A. Products with phosphoric acid are commonly used. The acid disolves the cement in the debris and makes it much easier to remove. Beware of any side effects on surrounding stucco and IG seals.
Q. What is used or recommended to wet the window in construction window cleaning?
A. High quality window brushs are used for their ability to spread adequate water without scratching the glass. They help prevent sand from getting trapped between the brush and the glass. Strip washers are also commonly used, but hold less water and carry a higher risk of trapping construction debris, which can scratch glass more easily.
Q. Can steel wool be used to clean glass in a construction enviroment, without scratching the glass?
A. Yes. Steel wool is sometimes used to remove construction debris from glass, but carries a higher risk of scratching glass. If construction debris gets trapped between the steel wool and glass, scratching could result. Also, if steel wool is to be used, use only new steel wool. If rust is present in old steel wool, scratched glass will result.
Insulated Glass Units (IG Units)
Q. What is an insulated glass unit?
A. An insulated glass unit, commonly refereed to as an IG unit, is two or more pieces of glass separated by a spacer to allow air or gas to be sealed between the panes.
Q. How are the surfaces of IG units identified?
A. The surface facing the exterior of the building is surface #1, the surfaces inside the IG glass unit are #2 and #3, and the surface facing the interior of the building is surface #4. (This is an example of a IG unit consisting of two pieces of glass.)
Q. On which surface of an IG unit is the tempering stamp usually located?
A. There is no standard or regulation specifying the location of the tempering stamp.
Low-E Coatings
Q. What are Low-E coatings?
A. Low-E coatings were developed to limit the amount of UV rays in buildings, which aids in the reduction of energy consumption. There are two main types of Low-E coatings, hard and soft. Hard coatings are usually applied during the manufacturing process of glass and are very durable. Soft coatings are usually applied after glass manufacturing and are applied in a vacuum chamber, usually with the sputter coating process.
Q. On which surface of an IG unit are Low-E coatings applied?
A. Soft coatings are located inside the insulated glass unit, on surface #2 in warm climates and surface #3 in cold climates. Hard coatings are usually applied on surface #1 or #2, depending on the application.
Heat Treated Glass
Q. What is heat treated glass?
A. There are two main types of heat treated glass, fully tempered and heat strengthened.
Q. What is fully tempered glass?
A. Usually just called tempered glass, fully tempered glass is a safety glass used in many applications where the possibility of human contact is high. This glass is 4-5 times stronger than non-tempered glass and breaks into very small pieces when fractured. According to Federal Specification ASTM C1048-85, fully tempered glass must have a surface compression of 10,000 psi or more, or a edge compression of 9,600 psi or more.
Q. What is heat strengthened glass?
A. Heat strengthened glass is twice as strong as non-tempered glass and must have a surface compression of between 3,500 and 10,000 psi, or an edge compression of 5,500 and 9,700 psi. Fracture characheristics of heat strengthened glass vary widely from much like annealed glass to similar to fully tempered glass. For this reason, heat strengthened glass does not qualify as a safety glass.
Q. What is safety glass?
A. Fully tempered glass and laminated glass are classified as safety glass.
Q. What is laminated glass?
A. Laminated glass consists of two or more panes of glass with a tough plastic interlayer made of polyvinyl butyral (PVB), bonded together under heat and pressure. Laminated glass is also used as an effective sound control product. Laminated glass is commonly used in airports, sound studios, schools and in houses near freeways to keep away unwanted noise from airplanes, heavy machinery and traffic.
Q. When was safety glass first required in houses and buildings?
A. The base requirements were established by the federal government in 1977 through the Consumer Product Safety Commision CPSC 16 CFR Part 1201.
Q. Where is safety glass usually located in a house?
A. Anywhere glass is more prone to human contact such as doors, windows close to the floor, stair landings and tub/shower enclosures. Check you local building code for details or more specific locations.
Q. How is tempered glass made?
A. Tempered glass must first be cut to the finished size, since it cannot be cut or modified after it is tempered. Then the edges are belt seamed or sanded to remove any sharp edges. Next it is washed to remove all fabricating debris. Finally it is heated to almost 1200°F and then quick cooled, which produces the temper.
Q. How do you know if glass in a window is tempered?
A. All tempered glass windows must have a permanent tempering stamp applied to each piece of glass to signify it is tempered. Click here to view an example of a tempering stamp.
Q. Where is the tempering stamp located on the glass?
A. Tempering stamps are located in the corner of each and every piece of tempered glass. Click here to view an example of a tempering stamp.
Q. Is tempered glass softer than non-tempered glass?
A. No. Tempered glass in not softer or harder than non-tempered glass.
Q. Is the surface of tempered glass rougher or more porous than non-tempered glass?
A. No. Quality tempered glass surfaces are just as smooth as non-tempered glass.
Q. Why are some tempered glass surfaces rough?
A. Poor quality tempered glass commonly has fabricating debris fused to it's surface during the tempering process. This is usually a result of tempering contaminated glass.
Q. Is there a standard for washing glass before tempering?
A. No. But, it is highly advised that all glass be washed prior to tempering to remove all fabricating debris.
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