STOP SCRATCHED GLASS: Window Cleaning Alert!onta

Scratched windows are a concern for general contractors and property managers alike.     

How does this happen? How can it be prevented? Should window cleaning contractors be responsible?

high rise window cleaning

To answer these questions, we must first understand the life cycle the glass on your building goes through.

There are several types of glass used for commercial buildings, including: plate glass (single pane), insulated (double-pane) and tempered glass (safety glass).

Tempered glass is used for its durability; it’s nearly five times stronger than standard glass and doesn’t break into sharp shards. Tempered glass withstands more wind, heat and impact before breaking. Because tempered glass is fabricated using extreme heating and rapid cooling processes, it is often referred to as a safety glass.


Fabricating or making tempered glass goes through four major steps.

  1. Sizing — measuring and trimming the glass to desired size and shape
  2. Edging — seaming the edges to create smooth, square edges
  3. Washing — completely washing the entire surface to remove loose debris created during the sizing and edging process
  4. Tempering — heating the glass in a tempering furnace approximately 1200 degrees Fahrenheit, then quickly drying it with a blast of cold air, reducing the temperature to 400 to 600 degrees

If loose debris is not completely removed during the washing phase of the manufacturing process; it’s likely to be baked onto the glass during the tempering process, making small bumps or “pimples” on the glass surface. Although it may not be clearly visible to the naked eye, these microscopic particles have become the leading culprit to scratched glass.

These particles detach during the normal window cleaning process and can cause major scratching, usually over the entire glass. Even during the construction cleanup of windows (removing plaster, paint, texture overspray, splashed concrete, mortar, tape and stickers), there is a likelihood that fused fabricating debris can be dislodged and dragged across the glass surface.

If you’re finding scratched glass after a window cleaning service, it’s more than likely due to defected tempered glass. Scratches made by fabricating debris have distinct characteristics, and are typically finer and more numerous than common scratches.

Damage can also be caused by subcontractors during the construction of the building. Likely causes are from:

  • workers placing ladders or equipment against the windows
  • masons smearing mortar on glass
  • painters dry-razor blading to remove paint
  • sanding perimeters of wood doors
  • lathers dragging wire lath across glass
  • tile contractors wiping tile grout off glass
  • interior texture contractors scraping excess texture on a dry window

For decades, the construction, window cleaning and glass industries have been using scrapers and razor blades as a standard in construction-related debris removal. More recently, however, these tools have been getting a bad rap and many general contractors have requested that window cleaners not use them at all.

Scrapers and razor blades, when used properly, won’t scratch uncoated glass and are effective at removing construction debris. Plastic scrapers, however, are not recommended because fabricating debris can become embedded into the plastic during the scraping process and will scratch every window it comes in contact with from that point on.

razor blade on glassrazor blade on glass
razor blade on glass razor blade on glass
Courtesy of IWCA:
Photos show a new razor blade before and after it was passed over the surface of defective tempered glass.

In most cases, when window cleaners are asked to use alternative methods to remove debris, instead of scrapers and razor blades, the result is often not satisfactory. Regardless of the cleaning method; expect that your window cleaning contractor will require you to sign a tempered glass scratch waiver.


While glass manufacturers are responsible for any fabricating debris found on tempered glass, window cleaners should be trained to use industry-proven methods and tools.

General contractors should select quality window manufacturers that will stand behind their products; even when scratch glass problems occur.

There are no regulations or standards in the window fabricating industry; even when it comes down to how the glass is washed prior to tempering.

Whether new construction or existing buildings, the International Window Cleaning Association (IWCA) advises window cleaners not to accept responsibility for finding fabricated debris defects on tempered glass. They also urge builders to waive responsibility for cleaners.

IWCA Tempered Glass Informational Bulletin: Scrapers & Fabricating Debris


Builders can test tempered glass when it is delivered and prior to installation; or fabricators can test as part of their quality control program, as recommended by the IWCA.

Ensuring defect-free, tempered glass should also continue on the construction job site after installation.

“Construction cleanup is the worst time to try to detect fabricating debris, or deal with a tempered glass scratching problem.”

A good window cleaning contractor will determine, prior to project start, if cleaning can be done safely, without risk of damage to the windows. Standard operating procedures must be in place and implemented before, during and after a window cleaning service.

Some testers believe thorough testing involves scraping the tempered glass (as it would occur during the normal cleaning process) and using bright lights to locate scratches. Magnifiers can be used to confirm they were indeed fabricating debris scratches.

Signs to identify poor-quality tempered glass:

  • Scratches and/or “pimples” are commonly widespread on the glass surface.
  • Scratching will typically occur on the side of the tempered glass that was in contact with the rollers in the tempering furnace.
  • The side facing up in the tempering furnace is usually defect free, and will not scratch when cleaned with the same window cleaning tools and technique.
  • If one pane has defects, it’s likely others will too if it comes from the same batch.

For more information on Metroclean’s Construction Cleanup services, please contact Ginger Rucker, Account Executive at (713) 255-0100 or

If you would like a free window cleaning estimate on your existing building, please contact, Director of Business Development, Lesli Mann at (713) 255-0100 or

“We’re listening to serve you better.”

“Construction Window Cleaning: A Primer by Daniel A. Fields”

“We’re listening to serve you better.”

### © Metroclean 2009. All Rights Reserved

Written by: Dahlia Kelada, Director of Marketing, Metroclean

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4 thoughts on “STOP SCRATCHED GLASS: Window Cleaning Alert!onta

  1. Socket Set January 24, 2011 at 10:55 pm Reply

    –. I am really thankful to this topic because it really gives great information ~*”

  2. Perth Window Cleaning October 18, 2011 at 3:38 am Reply

    Informative blog post. Dish washing liquid is a cost effective method of cleaning your windows.

  3. Window Cleaning Perth October 18, 2011 at 3:44 am Reply

    Good advice. People are often surprised when I tell them the secret to cleaning glass isn’t chemicals, its the squeegee.

  4. Abhijeet December 8, 2014 at 12:59 am Reply

    Nice stuff!

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