Accumulation of dirt, dust and/or other debris on the paint film; may resemble mildew.
Use of low-quality paints
Soil splashing onto siding
Air pollution, car exhaust and airborne dust collecting on house body and trim
If unsure whether the problem is dirt or mildew, conduct a simple spot-test with bleach.
Remove dirt with a scrub brush and detergent solution, followed by thorough rinsing with a garden hose. Heavier dirt accumulations may require the use of a power washer. Stubborn dirt may require the use of a degreaser or cleaner.
Paint with a high-quality paint that is formulated to provide superior dirt pick-up resistance