check out the Zanio page I posted and read the instructions. For their products they say wash with Dawn dish soap, clay bar, then polish. They have a hardener (for lack of better trems) that mixes with the polish to make it set up faster, it goes on thin and wipes off very easy. I have been using this stuff ever since my car was painted 15yrs ago. I very rarely wash it with soap and water anymore, mostly all I do is blow of the dust, wipe it with the duster, then wipe it down with their detail spray. Very good stuff If you think the windshield has overspray, the clay bar will remove it. But I would try some laquer thinner on a rag and rub it on the glass and see if it will come off first.