Clear Choice Window Cleaning employes the current industry standard for hard-water stain removal. We use of an oxide polishing agent, abrasive pads rated for glass and rotating electric buffer. The glass is first cleaned, then polished, than cleaned again, then a hydrophobic product is applyed to form a transparent, micro thin barrier to protect the glass against future water damage.
Glass Corrosion is an extensive topic. To aid you in your research on the subject we have included excerpts from this excellent article published in Window Cleaning Magazine issue #14.
Title: Understanding Glass Corrosion
By: Henry Grover Jr.
“Simply put, glass can and does corrode. It can be brought to complete dissolution by both acids and alkalis. Even rain water will corrode or etch glass. Water acts like an acid in that it is much more prone to selectively go after the alkaline compounds in glass. It does take many years. but its effects can be felt with your fingertip. The outside surface of an old storm window will always be noticeably more rough than the inside surface. Apart from corrosion by weathering, all glass surfaces are hydrophilic (water loving). So there is a molecular vapor on the surface at all times. Therefore, even the most smooth surfaces will have potholes and peaks about five microns across. These micropores can becomes filled with organic and mineral contaminants, which is literally bond to the glass.
Mineral deposits can and do cause corrosion. Water drops continue to reform and dry on top of the same deposits. Over time, this increases the pH of the drop as water evaporates. Once the pH goes beyond 9, total dissolution occurs. Both the reaction byproducts and the minerals in the water are left behind. They become concentrated around the outer edge of what I call the spot ring. When they are removed with an optical grade polishing slurry, the same shape of that ring can be seen as a clear distortion in the surface. This is especially noticeable on dark glass.
In view of this information, it makes sense to especially protect those glass surfaces that are exposed to concrete or brickwork runoff or ground water from sprinklers. This can be done with a quality hydrophobic sealant. A very regular maintenance program should also be followed, which might require intermittent removal of newly formed spots and replenishing of the hydrophobic coating, depending on the severity of the conditions.”