Glass surface attacked by deposits from the masonry?

Hello everyone,

I have the following problem: The glass surface of one of the windows on our house is clearly damaged from the outside. Over the entire glass surface, water streaks can be seen, somewhat like lime stains. These streaks cannot be removed with regular cleaning. I have also tried using thinner. My parents had this windowpane replaced many years ago because it was too badly damaged.

Interestingly, this phenomenon only occurs on a single window, which is located on the weather-exposed side on the ground floor. This location is unique to this window. Otherwise, there are only two windows on the weather side on the upper floor.

My suspicion is that the attacking substance comes from the masonry (brick) and then runs over the window. Something is also wrong with the brickwork because on the weather side the joints gradually come loose and fall out over time. The house was built in 1980.

Does anyone have an idea what could be causing this surface damage?

Of course, the stripes could also be on the inside, but two points make this rather unlikely for me: 1) The pane has already been replaced once. It would be quite a coincidence if this happened twice on the same window. 2) When I look very flat over the pane, I can still see the traces.

As I wrote above, the window has this position exclusively. The other windows are mostly protected by roof overhangs or are on the weather-shielded side.

I currently have the advantage that the entire window has just been renewed. So I have the old window for testing in case this effect occurs again in a few years. However, it appears to be a corrosion.

If you want to fix it yourself, there are probably only these two options:

Glass polish: for small, fine glass damage
Sanding down and polishing: for coarser glass damage

I will apply a glass sealant to the new pane, hoping that this helps or delays the effect. In 30 years there will be a new window anyway! ;-)