Scrapers and scratches

The process of making glass stronger can create surface particles; a cleaners' tool of choice can dislodge those debris
Matt Slovick
June 1, 2008

For years, people in the glass industry and the glass-cleaning business have debated the use of metal scrapers to clean windows, patio doors and curtain walls. One side says don't use scrapers; the other says scrapers don't scratch glass.

Most glass manufacturers, fabricators and contract glaziers say the metal scrapers can scratch the heat-treated glass that might have minute surface particles such as glass fines. Cleaners say the scrapers are the most efficient method of removing paint, caulk, concrete, dirt and other debris from glass.

"The issue is still outstanding from my point of view," says Cliff Monroe, senior manufacturing specialist, Arch Aluminum and Glass Co., Tamarac, Fla. "They're still cleaning glass with metal scrapers, and you don't do that in the glass industry with any type of metal device."

Monroe has been in the industry about 32 years and is the chairman of the Glass Association of North America's tempering division. "You would think with the technology we have in this world today, and between the IWCA [International Window Cleaners Association] and the glass industry, we could come up with some other means or method to clean glass related to a construction site," Monroe says.

The problem seems to be methods and, as in many businesses, money. It takes more time, and thus more money, for window cleaners to clean without scrapers and then go back and use a small blade to remove what's left behind. It takes time and painstaking efforts for contractors to complete their jobs without getting any debris on the installed glass. When someone puts a bid on a project, they budget the most cost-effective way to clean up. "Using a scraper is the easiest, quickest and cheapest method to get the window clean," says Sam Terry, the president of the IWCA, Kansas City, Mo. "The contractors are not willing to pay anything else. They don't believe it's an issue." Terry also is the owner of Sparkling Clean Window Co., Austin, Texas.

Scrapers technically don't scratch glass. But using a razor blade to take off a small sticker on a specific area is much different than using a 6-inch scraper to clean the entire surface of a window 6 feet by 8 feet. When a scraper hits a small piece of fabrication debris on a large piece of glass, it drags the debris along, thus causing scratches across the surface of the glass.

As an analogy, when you cut yourself shaving, is it the razor blade that makes the cut or the pimple on your face? Call it cause and effect. The glass is not scratched, a metal scraper is used to clean the glass, the glass is scratched. Some people, with scars for example, elect to shave with electric razors to eliminate cuts from a razor blade. And yes, electric shavers are newer technology and also more expensive than a throw-away plastic razor.

GANA, Topeka, Kan., has issued an information bulletin, Proper Procedures for Cleaning Architectural Glass Products, which discusses the use of scrapers. It states: "One of the common mistakes made by non-glass trades people, including glass cleaning contractors, is their use of razor blades or other scrapers on a large portion of the glass surface. Using a 2-, 3-, 4-, 5-inch and larger blades to scrape a window clean carries a large probability for causing irreparable damage to glass. ... When paint or other construction materials cannot be removed with normal cleaning procedures, a new 1-inch razor blade may need to be used only on non-coated glass surfaces. The razor blade should be used on small spots only. Scraping should be done in one direction only." The document includes a list of "Do's" and "Do not's" that includes "Do not use scrapers of any size or type for cleaning glass."

"The Glass Association of North America as well as individual member companies have reached out to the window cleaning industry and in particular the International Window Cleaners Association to help inform and educate professional window cleaners about today's architectural glass products," says Greg Carney, GANA's technical director. "We've made presentations at the IWCA annual convention, helped facilitate glass fabrication plant tours and allowed IWCA representatives to attend our glass fabrication educational seminars, all in an effort to help professional window cleaners understand why product technology has resulted in the increased usage of heat-treated glass and the inherent characteristics of these products."

Another bulletin, Heat-Treated Glass Surfaces Are Different, states: "The use of scrapers, abrasives, and harsh chemical cleaning agents is not recommended for any glass product because they can cause irreparable damage. With the best of intentions, window cleaners, and other tradesmen, may attempt to remove construction dirt and debris from the glass surface by scraping the surface. This can lead to glass damage, such as scratching and chipping if any microscopic particles have adhered to the surface and are dislodged and transported across the glass in the scraping process."

"Our informational bulletins and recent paper on Caring for Today's Architectural Glass (see Page 52), clearly acknowledge and address the fact that microscopic surface particles can randomly be found on the surfaces of heat-strengthened and fully tempered glass," Carney says. "We've also stressed that the glass heat-treating industry cannot guarantee or warrant that surface particles or other inherent conditions can be completely eliminated."

Glass fabricators, despite fastidiously cleaning and maintaining the machines that clean and heat treat the glass, cannot prevent minute, invisible particles from randomly occurring on the surface of heat-strengthened and tempered glass.

The demand for heat-treated glass has increased during the past decade due to the development of higher-performance tinted and coated glasses that must be heat-treated to avoid thermal stress breakage.

"We are up at least 40 percent-plus in the last decade," says Max Perilstein, vice president of sales and marketing for Arch Aluminum & Glass, about using heat-treated products. "Thanks to high performance low-E's like Guardian SN 68 and PPG Solarban 60, more outboard lites are getting heat treated than in the past."

Higher design loads require stronger, heat-treated glass to prevent breakage. According to members of the glass industry, a clean product is delivered to the job site, however, microscopic fabrication debris might be on the glass surface and is essentially undetectable until hit with a scraper.

Meanwhile, window cleaners continue to clean glass with metal scrapers, the same way they have for the past 40 years or more. Many window cleaners believe the debris on the glass is a result of poor fabricating procedures. Many refuse to believe that despite the fact that glass fabricators clean and maintain the glass washers and tempering equipment, random occurrence of surface particles on heat-treated glass will occur.

"I know the Glass Association of North America will continue to try to keep people from using scrapers on glass, which I don't agree with," Terry says. "It's not the scraper that's scratching the glass, it's the glass fines. Glass manufacturers need to follow the instructions on proper maintenance of their equipment such as washers and rollers."

It's quite a predicament for two industries involved in different ends of the construction process. The glass manufacturers and fabricators produce high-performance coated glasses that assist in safety, energy savings, human comfort and the attractiveness of a building. Before the ribbon can be cut, the window cleaners are called in to do their job. The result can be scratches on a few to all glass on the building. A new building at the University of Saskatchewan, Canada, needed three-quarters of its windows replaced as a consequence of cleaning. The scratched glass led to an incremental cost of $200,000.

Here is what some vocal window cleaners, say:

  • Scrapers are a standard technique for construction window cleaning
  • All construction window cleaners use blades and scrapers, which will not scratch glass.
  • All scratches come from defects on the glass.
  • The only heat-treated glass that scratches with 'metal' scrapers has excess fabricating debris on the surface as a result of poor fabricating procedures.

According to members of the glass industry, no equipment upgrade, cleaning or maintenance can eliminate the occurrence of fabricating debris because of the nature of the process. The large volumes of air used in the quench can create airborne particles, the glass seaming operation creates particles and the occurrence of glass breakage in the tempering oven all serve as a source of microscopic glass particles that will periodically end up in the oven or on the glass and get stuck to the surface of heat-treated glass.



Many glass washers today include a pre-spray area that removes debris even before it enters the washer, says a sales engineer at Billco Manufacturing Inc., Zelienople, Pa., which makes and sells machines that wash glass. With the high-performance glasses and coatings prevalent in today's architectural market, glass washers and tempering ovens must be of the highest quality and be properly maintained.



"Professional window cleaners have acknowledged that razor blades and other scrapers can disengage surface particles and entrap the material between the scraper and the glass surface, often resulting in scratches in the glass surface," Carney says. "As a result, the glass and glazing industry does not recommend or condone the use of scrapers to clean glass.



"The window cleaning industry has acknowledged that alternative cleaning methods exist and while more labor intensive, can be used in lieu of scrapers. Such cleaning methods are commonly used to clean other surfaces such as window frames."



The Canadian company City View Maintenance of Vancouver has found an alternative and has been cleaning windows without scrapers for more than a year. Rejean De Guise, who owns the company along with Howard Schuk, says the process involves powders and a paint-thinning product.



"Each time I introduce myself and tell [potential clients] I don't use razor blades, they are [thrilled] out of their mind," Guise says. "I use the expression 'new technology.'"



Although his process takes about double the time and triple the cost, Guise says he plans to expand his company since it is booking about twice as much business as in the previous year.



"We're not using blades, and it's such a relief," Guise says.



One solution the glass industry has tried is applied coatings. Pre-applied plastic films adhere to the surface with a temporary adhesive, static cling or both. They are typically removed by peeling the film from the unit. However, the films have the potential to lose adhesion. Site-applied liquid coatings can be applied by roller, brush or spray before major exterior construction and then peeled off. Grafted polymeric coatings are water-based and applied to the exterior of the fenestration or glazing assembly before shipment to the job site. The polymer cross-links into a solid protective film during the drying process. The coating bonds to the surfaces once cured. It's removed though a water-based "converter" that breaks the cross-linked bonds of the grafted polymer coating. It's then rinsed off with water along with attached debris. The converted coating is bio-degradable.



Some construction companies just use plastic or other means to keep the glass clean. However, this does not solve the problem of a future cleaning should fabrication debris exist on the glass.



Carney says GANA would like to work with the professional window cleaning industry to encourage proper protection of glass and window frames during construction and that only certain cleaning procedures should be used in the event of excessive construction debris.



"Working together we can ensure that glass continues to be the product of choice for windows, doors, skylights, railing systems and more and more decorative glazing applications - a trend that is positive for the professionals that manufacture, fabricate, install and clean today's architectural glass," Carney says.




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E-mail Matt Slovick at mslovick@glass.org.