Surfactant leaching
 
Cause

Many different water-soluble materials are used in the manufacture of latex emulsion paints. When these paints are applied during hot and humid periods and expected to dry during cool evenings, the painted surface will cool, allowing dew to form. This accumulated moisture on a paint surface whose curing is temporarily delayed will extract and concentrate different water-soluble materials from within the paint at the paint surface. As the water evaporates, a concentrated residue is left behind, causing staining, unsightly runs and gloss patterns.

Aluminum siding will react to temperature changes faster than solid wood siding because of the smaller amount of material involved. Consequently, aluminum siding will develop surfactant leaching quicker and more easily; however, all siding is prone to this problem under identical conditions.
 
Solution

Apply paint to all surfaces during climatic conditions that allow proper curing of the paint film. When “surfactant leaching” happens, flush with clean water immediately before the stains have sufficient time to set up or harden. Light scrubbing with a soft brush is acceptable. If stains cannot be removed in this manner, then repainting will be necessary during more favorable weather conditions.
 

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