An article by About.com
Painting your house exterior, you might find yourself staring in horror at your new paint color gracing the exterior frame of your vinyl windows. When painting your house, drips will happen; it’s just a fact of painting life. But drop cloths, plastic masking film, and dirt are really the only acceptable places for your paint to drip–not your window frame.
Most home remodel gurus advise you to use a single-edge razor blade to scrape the paint off.
But pay attention: they are only addressing the problem of paint on window glass. What about paint on the actual vinyl window frame? This is much tougher and the fix is imperfect. If you have light-colored vinyl frames, even if you remove the paint, some pigment will remain that is nearly impossible to remove.
For Big Drips and Globs
Let dry and peel off.
If you get a large amount of paint on vinyl windows, the best thing to do is nothing until the paint has thoroughly dried. As strange as it seems, the more paint on the surface, the better.
If you panic and try to clean off the paint while it is still wet, you might do more damage in the end. Smudging the paint will create an ultra-thin layer that later becomes almost impossible to remove.
After you let the paint thoroughly dry for a day or two, begin working the edge with your fingernail. The entire glob should peel off in one piece, leaving no trace. This will work whether on the vinyl frame or the glass.
For Roller Specks
Let dry and scrape off.
Smaller specks that are created by vigorous rolling will also come off, post-drying, with a plastic putty knife or fingernail.
Beware of using razor blades as they cut into the vinyl. It’s nearly impossible to regulate the angle of the blade on vinyl’s soft surface (glass is hard enough that the blade does not dig in).
For Paint Sprayer Specks
Wipe right away or sand with fine sandpaper.
These are tougher because paint sprayers specialize in atomizing paint very finely, so the specks on your window frame are not large enough to scrape off.
If possible, wipe off immediately. In most cases, this will not be possible because the specks dry instantly.
By this point, you are reduced to sanding off the paint from the vinyl with fine grit sandpaper in the #180 to #100 grit range.
Sandpaper will dull the surface of the vinyl, so you need to make a value judgement about which is more important: removing paint or retaining the surface of your window frame. Plus, sandpaper will not remove embedded pigment–unless you sand far into the vinyl.
Sand with fine sandpaper.
Smears happen when you drip on the window frame and then accidentally rub against it. As with paint sprayer specks, use fine grit sandpaper to remove the paint.