Hard water with mysterious source? Help!

Hi All,

I have an appartment complex that I do the office and rec building of quarterly, and they asked about hard water removal today. The odd thing is that there is no apparent source for the spots. They are mainly distributed near the edges of the frame, and it’s fairly consistent on the upper panes of the first floor as on the lower panes. They also have a fairly large overhang that should prevent rain from hitting them (thinking of run off from the building) and they’re too high for sprinklers. Any thoughts on what could be causing them? Also, for those that do sealants, how do you price them, and is the maintenance easier that just removing them every so often? Doesn’t the sealant build up and cause a much higher likelyhood of streaks? @Henry, @Steve076 you guys are two people that came to mind that would have good thoughts on this if you don’t mind weighing in. Any and all thoughts welcome! Thanks!

I am wondering about what material the exterior facade is made of. Is it stucco? I have seen pure water from a pressure washer leach minerals from stucco and deposit hard water spots on glass in only thirty minutes. They would not come off without a polish like cerium or a silica compound. The NG1010 is the best sealant. Will not cause any problems. And will absolutely help to prevent stains from sticking. You can do a 25 square foot mirror in about 15 minutes. Cost is about 11 cents per square foot. Just figure how much you want to make per hour and do the math.


One more thing. The stain looks like it has some color to it. Also it is mostly on the bottom edge of one window. I am wondering if someone sprayed that tree in the reflection?


@Henry Thanks for the quick reply! It’s pretty consistent over the building that is exposed to the weather, except for those that are covered by a 6ft+ overhang, except for the transoms in the pic. Its painted wood, no stucco. That is what has me stumped. It also doesn’t look like standard run stains off the building. Some of the lower panes do have more spots at the bottom of the pane.

Ahhh! I have also seen power wash companies use bleach to keep the green down and it reacts with the paint leaving deposits on the glass. Sometimes they will use a product based on sodium metasilicate and or sodium carbonate. This can leave stains that only diamond compound will remove. Look at whether they had the building power washed and then talk to that company. Try not to scare them in advance of gaining your info.


Good info @Henry, thanks! I will look into that. Would this not be removed by ettore scrub off then? I was able to remove some of them fairly well with it.

I am guessing if it is the result of those two sodium compounds then the Ettore product should not remove it. So I am guessing a reaction with the paint. A sodium deposit should also be white or off white.


i was wondering why the staining would be mostly distributed near the edges. Was thinking runoff somehow, but that wouldn’t explain why it was mostly near the edges. Why would it only be near the edges?

When I read what Henry said about how some pressure cleaning companies use products that can stain glass in a short time I have to wonder if the simple explanation is that the windows are rinsed in the middle while the pressure cleaning chemicals are allowed to dwell. The edges are close to the siding. Rinsing the windows off completely would rinse the chemical off the siding as well. So only makes sense that the middle of the windows are rinsed, not the frames/edges.

Could explain why only the edges have staining if pressure washing was done recently with chemicals that can stain glass.

It looks just like a property I do with the white residue splashing up off of the frame. Run your finger down the window frame and pretty likely white chalky substance will come off on your finger. Oxidation of the frames. I use Diamond Magic for the ones I clean. It gets all but the most stubborn mess off that is right against the seal and edge where the glass is. Old windows are a pain.