Mineral Deposit’s / Hard Water Stains
Hard water stains or mineral deposits can occur all the way up sixty six stories, or just on the first floor. They can come from brickwork, concrete facades, sprinkler systems, or the garden hose. When they form they can be extremely difficult to remove.
Hard water drops are hard because they are loaded with silicate based minerals.
These silicates usually include the elements silicon, oxygen, aluminum, iron, sulfur, phosphorus, potassium, calcium, and sodium. They are very similar to the chemistry of window glass, and so have the tendency to “lock on” to the microscopic surface.
Over time serious damage can be done. The reason lies in the anatomy of the spot.
As that drop evaporates in the hot sun the concentration of silicates increases, and so does the pH of the water drop. When the pH reaches 9 and above a chemical reaction begins leaching the hydrogen atoms from the glass surface.
Mineral deposits start developing on an invisible level. Then they become more and more noticeable until they are very unsightly and absolutely impossible to remove with a simple procedure. The greatest reason for this is, that such spots are very similar to the glass itself. They are based on a combination of silicates and silica. This is what the matrix of glass is. It is like trying to remove paint from paint.
Over time the exterior/weather side of window glass is attacked mostly by acid rain and is badly etched. Water vapor reacts with the elements that make up soda lime. Literally leaching away certain atomic components of window glass . You can actually feel this by lightly running a dry fingertip across the dry inside surface of a storm window and compare this to the outside surface of the same plate of glass. The outside surface will be much more rough.
Acids which etch glass should never be used to remove mineral deposits since these can very quickly and easily destroy windows. It is because of these reasons that the correct procedure for “clearing” windows of mineral deposits can be expensive.
So if your window cleaner tells you that it would be a good thing to “restore” your windows, it would be a good thing to listen.