Summer 2002

Coming Clean
Glass Manufacturers Answer Common Questions About 
One of the Latest Products to Enter the Market

With all of these new products on the market, you may be wondering if any of these glasses are right for your next project, and chances are you probably have a lot of questions about what these self-cleaning glasses can and cannot do. To help you better understand these new products, we asked each manufacturer to answer a series of questions about their products and their answers are printed below. 

Question:
How does your product work?
    AFG: Radiance Ti is a hydrophilic (water-sheeting), photocatalytic (self-cleaning organic particles) product.

    Guardian: Guardian’s low-maintenance coating is extremely hydrophilic (or water-attracting), which means water will sheet across the glass surface, rinsing dirt and debris away and leaving very little spotting behind as the glass dries. The coating is also scratch-resistant, which is a benefit throughout the window fabrication, installation and post-construction clean-up process. 

    Pilkington: Activ is a pyrolytic coated-glass product, thus the composition becomes an integral part of the surface, rather than being applied onto the surface after the glass has cooled. Once produced and installed, it never needs to be re-treated. 

The sun’s UV rays cause the integrated coating to react chemically with unwanted organic dirt to break down its adherence to the glass surface (photocatalytic effect) gradually and continuously. After installation, the integrated coating of Activ must be exposed to the sun’s UV rays for several days to become active. The integrated coating reduces the surface tension of water on the glass surface. This is known as the hydrophilic effect, and causes water to sheet on the glass surface, preventing the formation of separate droplets and ensuring that loose dirt and other particles can be washed away during normal rainy weather.

    PPG: SunClean glass is a coated glass product with photocatalytic and hydrophilic properties that combine to make windows easy to maintain. The transparent coating of SunClean glass is applied to hot glass during the forming process, where it forms a strong, durable bond with the glass surface. The photocatalytic property of the coating is triggered by the sun’s UV light and works to break down and loosen organic dirt slowly. At the same time, the coating’s hydrophilic property breaks down water beads and causes water to sheet over the glass, which helps to rinse away loosened dirt.

Question:
In what applications can the glass be used?

    AFG: Residential and non-residential glazing applications. 

    Guardian: We anticipate the primary application of this product to be as a low-maintenance glass option for the residential window market, typically in conjunction with high-performance low-E. However, the coating could be applied to certain commercial applications as well.

    Pilkington: Activ can be used in any residential or commercial fenestration application that is exposed to the outside environment with minimal overhang. Primary applications include residential windows, commercial/institutional windows and façades, skylights, atriums and sunrooms and as a part of exterior doors.

    PPG: It is well-suited for any application in which the exterior surface is exposed to the sun’s ultraviolet (UV) light.

Question:
Will windows with this glass ever have to be washed again?
    AFG: Radiance Ti works on organic dirt. Not all visual obstructions can be considered organic. This is a subjective question as everyone has a different opinion as to how clean his windows need to be. AFG’s opinion would be yes, but much less frequently, and in the interim (or between washings), the view through the glass will be clearer than with traditional glass products.

    Guardian: A realistic expectation for a low-maintenance glass product is to provide a cleaner and clearer appearance than the product would have without the coating, with low effort and less frequent cleaning than traditional glass products. It is important to set expectations properly. For example, while it may be technically accurate to describe a photocatalytic effect as self cleaning, unless the consumer would describe what they see as self cleaning, they’ll be disappointed, even if there is a demonstrable improvement relative to clear glass.

    Pilkington: Yes, though not nearly as often as without using Activ. If it has not rained for a significant period of time and the windows have become dirty, simply spray them with water and allow the hydrophilic effect to sheet away any dirt that has yet to be broken down. It is suggested that when spraying Activ glass, the windows should be rinsed from top to bottom. This maximizes the sheeting effect action by ensuring that all the dirt can be washed off and, on heavily soiled windows, reduces streaking issues in drying. 

If there is a heavy buildup of soil on the glass and it does not appear to be breaking down the dirt and/or sheeting it away when sprayed with water, then the integrated coating of Activ has been deactivated (i.e., the dirt has prevented UV rays from reaching the glass surface). Use a standard, but non-abrasive, window cleaner with a lint-free towel to hand-wash the glass. Then, rinse the glass thoroughly and allow several days for the coating to be reactivated by UV rays.

    PPG: Yes, the self-cleaning attributes of our product are effective in reducing the everyday dirt and grime that accumulates on the exterior surface, meaning windows will be easier to clean. However, inorganic materials, such as paint, will continue to require hand cleaning. If the glass becomes heavily soiled or does not become clean under specific exposure conditions and circumstances, then it will be necessary to clean the glass manually. Of course, the interior surface will need to be cleaned like any other window glass. 

Question:
What does it look like?  Does it have a color?
    AFG: Radiance Ti will be neutral in color. There will be slightly more reflectivity looking at the glass from the 
exterior.

    Guardian: The residential market has expressed a strong preference for color-neutral coated products. This preference is particularly relevant in the context of an IG unit that is now likely to include two or even three coated surfaces, providing a full range of value-added performance. Guardian considers color-neutrality to be a primary product design attribute and our low-maintenance glass offering meets the color-neutral standard exceptionally well.

    Pilkington: Activ has very much the same appearance as any other clear float glass used in windows and skylights. The only noticeable difference is that it may appear slightly shinier.

    PPG: From the exterior, windows with SunClean glass appear brighter. From the inside, they look the same.

Question:
Can the coating be damaged?
    AFG: Yes. 

    Guardian: It would be very difficult to damage the coating, which is nearly as hard as diamond.

    Pilkington: Yes, while the integrated coating of Activ will not rub off, it can be damaged if the surface of the glass is damaged. Also, it may become damaged if an abrasive cleaner or steel wool, razor blade or other metal item is used to try to remove stubborn, inorganic marks.

    PPG: Yes, that’s why proper care and maintenance of the glass are so important.

Question:
Is it safe for the environment?
    AFG: Yes.

    Guardian: Yes.

    Pilkington: Yes, the integrated coating of Activ will not degrade or peel off and damage the environment. 

    PPG: Yes, windows with SunClean glass should require less use of cleaning agents.

Question:
How does your product differ from other similar products on the market? 
    AFG: Radiance Ti is a hydrophilic photocatalytic product with a spectrally selective low-E coating. It is energy-efficient self-cleaning glass.

    Guardian: The Guardian low-maintenance glass product provides comparable or superior water and dirt management properties, while providing superior color-neutrality, optimal IG configuration flexibility and remarkable scratch resistance.

    Pilkington: There are no other products like Activ in the North American marketplace, so it is difficult to compare Activ to products that are not available. 

There are sprays and coatings that consumers can purchase to spray on their automotive windshields that cause water to bead that do not work well on vertically glazed applications. In addition, these sprays are only temporary and only affect how water reacts to the glass. These sprays have no self-cleaning properties.

    PPG: PPG defines self-cleaning glass as a product that has three distinct characteristics. First, the glass has a durable, long-lasting coating that has been fused into the glass at high temperatures during the glass manufacturing process. Second, the coating exhibits photocatalytic properties (i.e., it will slowly decompose organic material). Third, the same coating also exhibits hydrophilic properties (i.e., it will cause water to sheet over the coated surface and dry with minimal spotting and streaking). Other companies offering self-cleaning glass products should be evaluated as to whether they provide these three distinct characteristics. 

Question:
Is there a minimum angle at which your self-cleaning glass still works (as in a conservatory roof)?
    AFG: The photocatalytic self-cleaning glass works at any angle with UV rays. We have not defined the angle, but needless to say some gravity is needed for sheeting action. 

    Guardian: Technically speaking, no; the water management properties of this product will result in a cleaner, dry condition than uncoated glass, regardless of the installation angle. On a practical level, as the installation angle approaches 90 degrees (vertical), water moves more quickly off the glass surface, speeding the drying process.

Pilkington: We recommend that the glass angle should not be less than 10 degrees from horizontal.

PPG: The coating in SunClean glass will work on most exterior surfaces as long as the coating gets exposure to UV rays. Skylights and sunrooms are good applications. 

Architect's Guide to Glass & Metal