Most people are guilty of letting the housework fall behind a little bit; busy schedules of work, play and family take precedence over scrubbing and vacuuming. If the outside of your windows are becoming so dirty that you can't see through them, a regular cleaning product may not suffice for cleaning or may take too long to work. When used with caution and properly diluted, muriatic acid, also known as hydrochloric acid, can significantly cut down on cleaning time.
Wear rubber gloves whenever working with muriatic acid. Only clean the outside of windows with muriatic acid, as the fumes produced are harmful if inhaled.
Fill a bucket or other large container with clean water. Mix in 1 to 2 oz. of muriatic acid per gallon of water.
Dampen the bristles of a scrub brush in your cleaning solution, and scrub at the window stains. The acid will cut through thick stains like caked-on dirt or soap scum very quickly. Scrub carefully, as drips or splashes of the solution may damage skin, clothing or nearby plants. Continue to scrub until the window is clean.
Rinse the window with clean water from a hose or bucket to remove residual cleaner.
Dispose of the muriatic acid solution safely into a drain or other safe area where it will not be consumed by plants or animals.