Women Painters.com: Paint Issues and Fixes

Chalk Run-down:

The washing down of chalk from an excessively eroding paint onto another area below (a brick foundation, for example), ruining its appearance (see Chalking).

image courtesy of
The Rohm and Haas Paint Quality Institute

Possible Causes:

Use of a lower quality, highly pigmented paint.
Use of an interior paint for an outdoor application.
Erosion of factory-finished metal siding.

Solution

Remove as much of the chalk residue as possible (see Chalking). Scrub any stained areas with a stiff brush, using a detergent solution; rinse thoroughly. In cases of severe staining, an acid wash may be necessary. Either way, if the affected area dries to a different color, consider painting it with a quality latex paint. Eroding aluminum siding should be thoroughly cleaned (power washing recommended) before painting with a quality exterior latex paint.