Are you sure it is exterior? Can you feel it on your fingers?

Thanks for responding. I updated with photo. It feels chalky and looks like the fake spray on snow.

Was the home recently painted? How good are you with a razor blade?

I tried razor blade but still there. No new paint. Looks like white residue from white window trim.

I had similar white "stuff" on my windows, the only thing that cleaned them was bar keepers friend (powder) and lots of scrubbing. I had to do it twice but the windows looked perfect after it. These were basement windows that had sprinklers hit them all the time.

Try a Mr clean magic sponge thingy. I had mineral deposits on my windows when I moved in from well water. The sponge took it off. You might have to use a little elbow grease.

Thanks everyone for suggestions. I’ll get to work and post results.

Spray some WD40 and then use the razor blade, let us know which works for you

This stuff is the best that I have found for removing pretty much any build-ups on glass...see description below.

http://www.jracenstein.com/category/00016A1/a1-hard-water-stain-remover/

Use in the removal of silicas, cement leach, acid rain and mineral deposits from glass and the other exterior surfaces and interior surfaces like tile and shower doors. A nontoxic, water-based biodegradable SOFT CREAM. Contains no acids or abrasives. Cleans and polishes aluminum, fiberglass, and painted wooden frames and mouldings. Non-Toxic. Biodegradable. Easy to apply with a white scrub pad, felt pad or fine steel wool. Apply by hand or with an oscillating buffer (8,000-11,000 rpm). Tested, approved, and now in use by some of our biggest and best stain removal customers. Covers 400 - 500 sq. ft with one pint.

If it’s paint overspray try spraying with rubbing alcohol and then scraping.

Hi Michelle can you tell us more about this mud? What is type of this structure? I would not advise you to use WD40 for your window, after applying it, you may see ugly spots that are difficult to remove. Try using an acetone solution, test it on a single window to see the result. The acetone itself is very concentrated, so you should to mix it 1 to 1 with water and for safety use rubber gloves. And one more thing buy good and high quality window cleaning equipment South Africa. All the best

So WD40 is bad, but Acetone is better? No offense, but acetone can melt a lineal of some windows if left on it long enough.