The Destructive Power of Acids
Unfortunately most building owners, property maintenance managers, and even window cleaners are not aware of the destructive power of acids. The general opinion is that windows cannot be harmed by acids. That even when windows become seriously stained by hard water as is shown here in these two pictures, all that is required is a quick "acid wash".
Little do they know that chemicals such as hydrofluoric, sulfuric, and ammoniumbifluoride have a detrimental effect on the window surface;...every single time!
Acids and Dark Glass
Actually there are an assortment of acids and alkalies that react with glass surfaces. Hydrofluoric acid however is probably the most common. This is the one which has been favored by the window cleaning industry for many years. It has been added to so called professional glass restoration products. Companies have even used it pure in much higher concentrations. The destruction caused by this acid can be seen all over the world in every country. Based on what I have personally seen in the field it has had the greatest effect on dark glass. That is glass that is tinted with different metal oxides all the way through from the inner surface to the outer surface. The full thickness in other words. I believe that dark glass is most easily "dissolved" by hydrofluoric (HF) acid. HF will "eat away" at the surface leaving behind clear impressions of hard water spots. This causes a type of "orange peal" effect. If used to remove long drips of a concrete sealant this results in a "banding" effect. Any light scratches that might have been covered over and hidden by newly formed hard water spots are fully revealed and become magnified fifty times. On occasions these are difficult to see unless the sun is shining directly on the glass. So they become visible when the sun moves around to that side of the building or comes up the next day. It is also possible that the surface could take on a patchy/cloudy etch. Again this could be rather light or very intense depending on different conditions present at the time the acid was used. One other effect I have not wrote about yet involves a change in both the chemistry and the physical properties in the glass surface. When glass is exposed to HF it becomes very prone to scratching. So glass that was previously very smooth and resistant to scratches now becomes very rough and easy to scratch. Making it that much more difficult to maintain over the course of its life.
Acids and Clear Glass
All of the effects mentioned above also apply to clear glass. Just not as intense in my opinion. Although it is true that both hard and soft low e coatings are much more frequently used these days on the first surface of clear glass. The trend also is for these coatings to be very transparent. So it is very difficult to know they are even there. You would have to test the surface with a device or some other way to determine if it had a coating. Companies have come up with coatings that are supposed to have photoreactive and even photovoltaic properties. Any of these high tech coatings would be destroyed by the first time use of these different acids such as and especially HF. I have include below a picture of the kind of damage that is caused by the use of HF on an old coating from PPG called Solar Cool Silver. This coating was literally stripped off by HF and is now impossible to repair. The windows on this building have been permanently destroyed.
This Bulletin is published in this blog for the general public. Not that this information is necessarily known by all window cleaners. Because it is unfortunately not. The sad truth is that there are thousands of window cleaners that do not know and or simply do not accept this information. The ability to make a quick buck coupled with the desire of the building owner to save thousands of dollars, has driven the widespread use of acid. The cost of properly and correctly restoring a window can easily be ten times the cost of clearing it with an acid such as HF. The risk of losing a window here and there or even all of the windows is seen as the price that must be paid to save all that money. This is rather faulty reasoning however. For if you must replace the windows because of acid use the stains will still return. The old and or new windows must be sealed with the correct product and then the windows must be properly maintained. The ultimate cost of window replacement could be very expensive. Much more then having a proper restoration performed or certainly much more than a quick acid wash. If you are looking for more information on this subject just send an email to henrygroverjr@gmail.com
Written by Henry Grover Jr.
If you would like to receive these posts direct to your inbox just type your address in the box at the top right, "Follow by Email".
No comments:
Post a Comment