When dealing with windows that have hard water stains on them, we follow a tried a true method to ensure best results. The following outlines this on a recent job of office windows.
Each window needs to be individually washed, chemicals applied, scrub , wait 19 minutes to dry and then clean. This procedure is normally done twice to ensure most of the mineral stain is removed.
After the stain has been successfully removed, we also provide a conversational wash to move all excess chemicals.
Of course, a regular window maintenance program will prevent the problem recurring.