Even if you have some of the same paint you originally used, it can be tricky to go back later and seamlessly touch up a painted surface. Whether you're touching up over a wall repair, covering a water stain or repainting a nail-pop on a ceiling, you'll need the right primer and tools to make the new paint blend in with the old.
Save Your Paint
Label, date and save paint from every painting project. Keep it in a dry place protected from freezing. If space is an issue, save the lids or labels with the color, type of paint, and where you used it. Typically, it is easier to touch up with better quality and flat paints. Cheap and glossy paints can be trickier and more likely to result in "flashing," a term that describes the difference in sheen between the existing paint and the touch-up paint.
When touching up paint over a repair, it's critical that you use a primer or sealer first. If you paint directly over the repair, you'll be left with a flat spot because the repaired area will soak up more paint. For most drywall repairs, a general-purpose, water-based primer works. Use a shellac-based sealer for water stains or stains from crayons or oily substances. Shellac sealer is available in spray cans, which are convenient for small touch ups.
Whenever possible, apply the paint with the same tool originally used to paint the surface. If you brushed on the paint, use a paint brush for touch up. When touching up over a wall or ceiling repair, use a small roller with just enough paint to apply one or two uniform coats. Touching up a wall that was spray painted can be harder--use a roller with a very short nap and apply the paint as thinly as you can for the best results. When using using both a brush and roller, "cut in," or paint around windows, baseboards, corners, etc., with the brush before rolling to minimize the appearance of brush strokes.
Temperature and Drying Time
Assuming you are touching up with water-based paint, apply it when the temperature is at least 50 degrees Fahrenheit. Keep in mind that paint changes color as it dries, usually becoming darker. You won't be able to tell if the new paint has blended for about an hour, or until the paint has dried.
When the Paint doesn't Match
If the touch-up paint does not match an existing wall surface, paint the entire wall from corner to corner. Even if the new paint color or sheen is a little different, it will appear to match the other walls perfectly after it dries.