Accumulation of dirt, dust particles and/or other debris on the paint film; may resemble mildew.
Use of a low quality paint, especially lower grades of satin or semigloss.
Soil splashing onto siding.
Air pollution, car exhaust and flying dust collecting on house body and horizontal trim.
Wash off all surface dirt before priming and painting, using a scrub brush and detergent solution, followed by a thorough rinsing with a garden hose. Heavier dirt accumulations may require the use of a power washer. While dirt pickup can’t be eliminated entirely, top quality exterior latex paints typically offer superior dirt pickup resistance and washability. Also, higher gloss paints are more resistant to dirt pickup than flat paints, which are more porous and can more easily entrap dirt.