Touching up a gouge or defect on a painted wall is more complicated than it seems, and in some cases, you may not be able to do it satisfactorily. A proper touch up isn't just about matching color, but about matching sheen, texture and even application method. In addition, drywall absorbs touch ups differently than finish coats. Glossy paints are the the most difficult to touch up, and one that has been applied by spraying is virtually impossible.
A proper touch up involves more than simply brushing a coat of paint onto a defect with a paintbrush -- if that makes the defect disappear, you should invest in the lottery to take advantage of your lucky streak. A professional touch up requires a strategy that begins with examining the color, sheen and application method of the existing paint so you can gather the proper tools and supplies to duplicate it. In most cases, you'll want to opt for a roller -- not a paintbrush -- to duplicate the texture of the existing paint. Dabbing with a foam brush is often an adequate touch-up method for small spots on a rolled wall.
Dilute the Touch-Up Paint
It's axiomatic that the touch-up paint must be the same color as the wall paint, but even if they're from the same can, the touch-up paint may dry slightly darker or lighter, simply because drywall absorbs paint differently once it has already been painted. One way to mitigate this problem is to dilute the touch-up paint with 5 to 10 percent water, which slows the drying time and provides assurance against premature drying and darkening. If you had the foresight to save a small amount of the wall color for touch ups, diluting it is especially important, because it has probably thickened while in storage.
Make Wall Repairs
The reason a wall needs a touch up is often because of an impact that created a gouge; proper repair of such damage contributes as much to an effective touch up as the paint itself. In most cases, all the repair requires is an application of drywall joint compound or a small piece of drywall tape covered with two or three coats of joint compound. After scraping the repair, examine it from several angles with a light while you're sanding, and erase all humps and noticeable scratches. Complete the repair by coating it with a single coat of drywall primer, preferably applied in the same way you apply the topcoat.
The Touch-Up Procedure
The touch-up procedure isn't a difficult one and doesn't take much time.
• Clean dust from the wall around the spot you're touching up with a lint-free cloth. • Apply the paint with the same type of tool the painters used to paint the wall. In most cases, this is a roller, but if the paint has no discernible texture, it was probably sprayed. If so, it's best to touch it up with an air spray gun or a handheld airless one. • Shine a light on the touch up after it has dried, and examine it from several angles. If the edges are visible, dilute the paint a little more and redo the touch up, covering a slightly larger area.