Developing Products for Maintaining, Restoring, and Protecting Glass Coatings

Written by Henry Grover Jr.
Member of the IWCA Glass Committee

Why Maintain Coated Glass?

In the Vitro Glass Technical Document TD-142 on page two under the subtitle "Cleaning Solarcool® and Vistacool® Coated Glasses" it says quite plainly that "Acidic cleaning solutions are not recommended.  Use only mild soaps or detergents.  Abrasive cleaners, fluoride salts, or hydrogen producing compounds are not recommended. In addition, because fingerprints, stains, smears, dirt, scum, sealant residue, scratches, and abrasions are more noticeable on reflective glasses than on non-reflective glass, take extra care in handling and cleaning the glass.  Finally, Solarcool® and other coated glass that is glazed with the coating exposed to the outdoors should be cleaned more frequently (a minimum of 3 to 4 times per year). Materials, such as rundown from metals and masonry, such as concrete, stucco, etc. should be cleaned from the glass as soon as they occur so that they are not permitted a long residence time on the coated glass surface. If such rundown is not quickly removed, permanent staining and/or glass damage may occur. It should be understood that while such rundown residue will be more noticeable on reflective glass, it can also occur with uncoated glass, resulting in similar permanent staining and/or glass damage."  In my opinion this information can easily be extended to both hard and soft coat low e surfaces.  Especially soft coats that are exposed to the weather on the number one surface.  Such material deposits can be very easy to remove if done promptly.  For example concrete, silicone caulk, and silane sealants go through a "cure time".  During which they actually bond to glass and or glass coatings.  I have done experiments with concrete that very plainly proved this.  I was able to actually push hardened concrete off the window within a couple days, but after a week or two it had become part of the glass.  Silicone caulk cures in only several hours.  Before it cures it can be wiped off with a solvent.  As a consequence maintenance during construction is much more critical because of this behavior.  Once construction is complete the windows should still be frequently inspected in order to establish a practical cleaning frequency.

When Does Coated Glass Need to be Restored?

Coated Glass Restoration

Coated glass is in need of "restoration" when contamination residues such as concrete, silicone caulk, or silane runoff does not come off with a simple cleaning using either soapy water, and a squeegee; or pure water window cleaning equipment.   It also is in need of restoration when it becomes stained with mineral deposits, which result from either poorly aimed sprinklers, ground water or concrete runoff.  This is because many of the tools, chemicals, and abrasives that can be used on glass surfaces just cannot be used on coated glass.  After reading the Tech Doc above it becomes obvious that there is very little that can be used to "restore" such coatings.  Razor blades, steel wool and bronze wool should never be used.  Even synthetic steel wool should never be used in my opinion.  Although synthetic wool is based on much softer plastic fibers or filaments; this plastic is loaded with abrasive particles that might scratch the coating.

Alternative Products for Restoring Coated Glass

We already have many products that are quite safe and effective for maintenance cleaning of coated glass.  Mild soaps and detergents along with soft applicators and squeegees are perfectly safe to use on coated glass.  Purified (deionized) water and the brushes used to apply, scrub and rinse it away are certainly safe enough to use on coated glass surfaces.  Restoration is somewhat more difficult.  I don't know of any commercial products that have been developed specific to the removal of silicone caulk, paint, concrete, or hard water deposits from coated glass.  Most Window Cleaners use their own "discovered" products to do this.  High quality super-abrasives such as cerium oxide are quite effective and safe for removing hard water spots with the right technique.  But stay away from crude abrasives or commercial products based on these.  They will scratch coatings.  Cerium powders can be very expensive.  The particle size must be well controlled.  You will want a white powder with an average particle size of 3.5 microns at a purity of 99.9%.  The techniques for removing mineral deposits from coated glass are also critical.  Always remain completely flat on the plate at all times.  I suggest a soft natural felt pad.  Also use a rotary polisher/motor between 800 to 1200 rpms.  There are also optical grade microcrystalline silica powders out there around the same size and purity rating that are a third or less the cost of cerium, but most of these are not as effective at removing deposits as quickly as the cerium, and time is money.  Functional cleaning compounds can be made using any of the superabrasives.

Abrasive Cleaning Compounds

Composite abrasive powders which utilize plastics are effective at removing silicone caulk, wood stain, silane runoff, and paint.  There are also other more eco-friendly alternatives such as powdered walnut shell, or corn cob.  These can be used in different ways.  They can be blended with some of the newer more powerful organic solvents which are water miscible, so that you get the best of both worlds.  The grinding and cutting action of the abrasives, which are softer than the glass coating but harder than the material you are looking to remove, as well as the softening power of the liquid organic solvents.  Sometimes the two can be blended together in a hybrid compound.  The particles should be between 25 and 150 microns.


Another application of both super-abrasives and composites are "Slow Release Pads".  These are based on a plastic which, when put in contact with water or water based organic solvents, will slowly break down and let go of the particles.  The particles can either be super-abrasives like cerium oxide or composites that utilize plastics.  But once again I strongly suggest doing a test on specific glass coatings before employing any of these hybrid high tech solutions.  

Three Different Products for Protecting Glass Coatings

So far we have discussed maintenance and restoration of glass coatings.  The last subject is that of protection.  There are many different types of products that can be used for protection.  The first is a plastic film applied before the windows even arrive at the job site.  This product can be left on while the windows are in storage.  It is also left on while the windows are installed.  Then after the construction is complete it is easily pealed off leaving a generally clean surface.  I have worked with it on a post construction residential.  The only problem I had with it is the static shock I got if I pulled it off too quickly.


The second is a product similar to the first that can be sprayed on once the windows are at the job site.  It can also be rolled on like paint.  General Chemical has a product like this.   Once again however I suggest doing a patch test to make sure the product will work for your aplication.  These two different types of products are very effective at protecting the glass coatings (or even plain glass), but are only temporary.  They block vision and so must be removed at some point.


The third type of product is a wipe on product/sealant which goes on invisibly.  It is intended to be permanent.  We are already familiar with these hydrophobic (water hating) products for glass  Their main purpose is to guard against hard water spots.  Some are definitely better than others.  But they were developed specifically for glass surfaces.  None that I know of were developed specifically for metallic oxide glass coatings.  It is also true that some of these glass sealants will not work on coatings of this type.  Some like Rain X do work well.  Those that do not are based on a chemistry that was designed to form covalent bonds with the reaction sites of glass, not metal oxides.  I know of chemical companys that specialize in this type of chemistry.  They would be more than happy to work with any of our manufacturers in developing a product of this type; specific for glass coatings.

You now have the opportunity to JOIN the IWCA and expose yourself to top notch glass surface education, training and research. Volunteer to join the glass committee and contribute your experience to a growing body of knowledge that is benefitting the worldwide window cleaning industry.  There is so much that everyone of us can contribute.  Be a part of something that is truly historic!

Written by Henry Grover Jr.
Member of the IWCA Glass Committee
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