It is relatively easy to remove light stains with almost any polishing system. But there are very difficult stains that require much more advanced techniques to effectively and completely remove. One way to determine if the spots have been completely removed is to fog over the new surface with either our breath or a steamer. If the residue from mineral deposits is still present you will be able to see it. Otherwise you will see only a light film of vapor. Spot residue can also be felt with a dry fingertip.
One system involves the use of a circular sponge like pad that is connected to a rotary machine. The RPMs are between 1,200 and 3,000. The faster the machine the quicker the spots will come off. Obviously. Although this has the tendency to dry out any lubricant such as water much quicker. There is also a greater chance for creating zillions of little scratches by picking up any stray silicate particles from the surroundings. This is also why it is critical to very thoroughly clean the surface before polishing. The pads used are around six inches in diameter. In my experiments I determined that rotary machines are definitely more effective than random orbitals or random oscillators (which are square). The random oscillators however are very effective at getting into the corners. They also have the feature of not throwing the compound/slurry all over your work area. You can work right up to the adjoining plate without getting anything on it.
Now while the exact compound is indeed critical to the performance of the system, it is also equally important to use the correct polishing pad. There are reasons why people are having more success with steel wool pads over softer sponge-like pads. Very simply put it is the steel strands that drive the polishing particles down into the surface. How far they actually carry each particle is quite another matter. But obviously they are dragging these particles some distance since the surface is being polished. Let me relate an interesting discovery I made when looking at scratch removal techniques. At the time I was playing with a 10,000 RPM Dremel motor. When using a half inch hard felt bob and diamond compound around five microns I was able to remove fine line scratches;...slowly. Of course it would jump around some. But with a strong careful hand it could be done. Then I went to a hard wooden bob. Everything else was the same. The wooden bob was about three eighths of an inch in diameter. It was able to remove stock in a fraction of the time that hard felt bobs needed. And left a wavy furrow where the scratch line was. But that wavy furrow was perfect. Although it was even more of an eyesore that the original scratch! My point here is that speed coupled with high pressure can make a tremendous difference in the results. The same speed that is obtained form a half inch bob moving at 10,000 RPMs can also be obtained from a six inch circular pad moving at 1,500 to 3,000. There is a formula for calculating the number of feet per minute of any point on the outer edge of the pad. When you do the math you will see what I mean. To obtain the same pressure it is necessary to minimize the contact area as much as possible and go to either a hard felt ring or a wooden ring. I am still in the process of experimenting with this idea. Although I have built what I call a Gyro Wheel that uses a hard felt ring with a six inch outer diameter and a four inch inside diameter. The ring is about a half inch deep with a width of one inch. The compound is applied as drops directly to the wheel that is then applied to a window which has been wet with soapy water or some other lubricant for polishing. This quite effective at removing average hard water spots. The compound can be an optical grade silica, a cerium, aluminum oxide, or even something more esoteric like diamond, tin, or even silicon carbide. There are many different polishing powders out there. Any of which can be formulated into a holding very thick compound. This is another part of the technology. The particle. Different particles will absolutely give you different results. Take cerium for example. It does most of its work by rubbing. It also reacts chemically with glass surfaces. Now diamond on the other hand along with silicon carbide cuts. Each has particles with very sharp edges. Each is also harder than glass. However because of this diamond compounds have the tendency of leaving what I call an abrasion haze. This might be invisible on overcast days or the shadowy side of the building, but will show up brilliantly in the direct sun. Another interesting idea is to combine different powders to obtain varied effects. Another idea is to create a wooden ring that is also six inches in diameter but has in inside diameter of five to five and a half inches. This would greatly increase the pressure and hence the efficacy of the overall system.
As I continue to develop the technology of stain removal I will be writing about it. Although not everything will be included in this blog, on my Surfaces Sub-Forum, in the WCBO, or any other publication for the Window Cleaning Industry. Since my desire at this time as it always has been, is to establish my own newsletter which I will be publishing online. It will focus on advanced techniques for removing and preventing hard water stains.
Written By Henry Grover Jr.
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