If you're like us, you'd like to paint the house once and forget about it for as long as possible. But mistakes can happen all through the process, and many of them can affect the coating's longevity, says the Paint Quality Institute, the educational arm of the manufacturer Rohm and Haas. Here are the most common ones, how they happen, and how to recover. But if your home was built before 1978, older coats of paint may contain lead. To learn about the precautions you should take, read our June 2006 report on lead paint.

Alligatoring

The breaking apart of a coating in a pattern resembling an alligator's skin. Causes: For oil-based paints, the natural aging process could be to blame. But with newer, water-based paints, mismatching paint types from one coating to the next or applying one coat before the previous coat has dried are the most likely culprits.
What to do: Completely remove old paint down to the bare surface by scraping or sanding.

Mildew

Dark, spotty growth from the formation of fungus. Causes: Sides of the house that are shaded remain relatively damp. Or the paint lacked mildewcide, there was insufficient mildew removal before the last painting, or bare wood was painted without first priming.
What to do: First, ensure that it's mildew by touching the area with a few drops of bleach; mildew will disappear, dirt probably won't. Treat with one part bleach to three parts water (wear eye and skin protection). After 20 minutes, apply more as it dries and scrub. Rinse well, prime, and apply a mildewcidal exterior paint. See our Ratings   for models that resisted mold growth.

Chalking

Fine, powdery buildup on a painted surface that sloughs off dirt. But if it's heavy, it can shorten the life of the coating. Causes: Some chalking can be expected, but excessive chalking can result from using an inferior or inappropriate paint--say, an interior paint applied outdoors.
What to do: If repainting, first remove as much residue as possible, either through scrubbing and rinsing or powerwashing. If some chalk remains, prime the surface.

Color change

Also called fading, any premature washing out of a paint's color, typically on the sunniest side of a house. Causes: Chalking can contribute. So can using an inferior or inappropriate paint, overtinting, and using certain bright shades of primary colors.
What to do: Use a higher grade of paint next time. We've found that premium latex paints outperform most lower-cost paints. See our Ratings  for models that resisted color change. If fading results from chalking, remove it (see above).

Cracking

Another form of paint breakup that occurs at least on the outer coat, it leads to flaking. Causes: Using paint with poor adhesion, poor surface preparation (for instance, painting bare wood without priming), or painting in cool or windy weather, which dries latex paint too quickly.
What to do: If only on top coat, scrape off loose paint, lightly sand, prime bare spots, and repaint. If cracking goes to the wood, remove all paint, fully prime, and repaint.

Peeling

Substantial loss of paint, either down to primer or all the way down to painted surface, from poor adhesion. Causes: Painting a wet surface, moisture from behind the wall, inadequate prepping, or using a low-quality paint.
What to do: Eliminate source of moisture, prepare surface properly, prime and repaint with one of our highly rated paints.

Read our complete Ratings report and related information on exterior paints & stains .