by Henry Grover, Vision Glass Detailer
From eClean Issue 23
If you drive down any highway system on a sunny day, you will notice the glass on some multi-story buildings is actually quite wavy. Look for buildings that have the glass flush with the concrete façade.
Acid rain (which is a worldwide problem) literally reaches deep into the pores of the concrete leaching out various silicates. Loaded with these minerals, the rain runs down over the glass leaving behind mineral deposits as it dries in the hot sun, which are chemically very similar to glass. Such deposits become locked into the micropores of the window glass. These hard water spots go all the way to the top of multistory buildings.
Can you imagine 44 floors of windows totally covered by stains? One building can easily cost $50 thousand to professionally restore, whereas a simple window cleaning might only cost one to two thousand dollars.
In order to sell the restoration job, a company must be able to guarantee that the stains will not return. This can be difficult, if not impossible, for most. For this reason, along with the expense of professional restoration, cleaning contractors along with building owners opt in favor of doing what is called an acid wash. No guarantee. Stains will return, but the overall cost will be close to what a simple window cleaning would be.
The windows are cleared this way year after year. Each time just a little more of the glass is taken away! Ultimately, the building becomes wavy.
This effect might happen the very first time due to various circumstances. Acids can also turn many plates a milky white. Either way, glass etchants always create surfaces that tenaciously hold onto new spots with a vengeance.
Acids can very easily degrade the physical integrity of reflective first surface pyrolytic coatings, creating a situation where the coating can be stripped off in patches the next time the acid is used. Even polishing compounds can strip off acid damaged reflective coatings.
The use of certain acids on pyrolytics create another problem. That is, if there were any scratches left behind from a previous ‘restoration’, these can and usually are covered over with new deposits.
Second time around the acid will remove such deposits, and at the same time greatly accentuate the old scratches, which now will stand out really bad in the bright sunlight from the inside looking out. This effect can be
totally missed from the outside looking in.
Considering all things, why would anyone want to use acids? Simply, that they work almost every time, and they do it at a price very close to what it would cost to just run a squee-gee. This satisfies the cleaning contractor and the building owner. The problems explained herein are usually unkown.
Hard water stains can also be left from sprinkler systems carrying ground water. Ground water is also loaded with silicates due to acid rain.
The burning of hydrocarbon fuels releases certain gases into the air that react with rain making it very acidic. As rain seeps down into the ground, it reacts with the minerals there. Breaking them up and bringing them into the ground water systems, which are used to water lawns and clean vehicles. Sprinkler heads are put too close to the windows. As a result windows become covered with hard water spots.
When buses are cleaned and rinsed with ground water, they collect spots. I haven’t found a travel bus yet that didn’t have hard water spots all over the front, side, and rear windows.
Other than the use of acids, how do some people remove hard water stains from their windows and vehicles? The green solution involves the use of polishing slurries such as cerium oxide. Unfortunately, the correct technique is often times missed.
To cover many square feet in very little time, large rotary felt wheels are used. They are dampened and the edge of the pad is loaded with just the right amount of dry cerium from a box. Then the pad is used to rip into the glass edge on. This will remove the stains very fast but also leaves zillions of microscopic scratches which show up in the direct sun as an abrasion haze.
There are, however, some very good commercial systems that use wet slurries, and bonded superabrasives. Most use rotary motors that run polishing disks. (See
Some effort is put into eliminating what is called the “bobbing effect.” This is difficult to do since the wheel wants to grab on one side. To completely eliminate the bobbing effect, maximize efficiency, and minimize abrasion haze, it is necessary to keep the polishing pad completely flat on the glass at all times. This can be done by putting a universal joint between the drive shaft of the rotary motor and the polishing disk.
I use a six-inch aluminum disk that I have cut six large holes in around the center. I also use a six-inch hard felt ring instead of a circular pad. These two alterations move most of the weight to the outer edge giving the polishing wheel gyroscopic properties.
A fail safe collar keeps the potential angle of the drive shaft at about 12 degrees. The key to a truly efficient polishing system for engineering precision surfaces involves the correct matching of machinery to superabrasive technology. Professional window glass restoration is not an acid wash. The next article will focus on selling professional glass restoration.
Henry Grover Jr. specializes in product development for companies that perform glass restoration. He also writes an online newsletter called the Vision Glass Detailer (VGD), which is available free for the asking at henrygroverjr@ gmail.com