Low-Impact House Wash. Pressure-washing is fast and effective, but it can also be destructive. If you're not in a hurry, Wet & Forget offers a gentler alternative. According to the maker, you can apply this noncaustic, nonacidic cleaner to any exterior surface and let the wind and rain handle the scrubbing and rinsing. The company cautions, however, that it often takes two to three months to get rid of stubborn stains like mold and mildew. A one-gallon jug costs about $30. Wet & Forget, 888/727-8524, wetandforget.com