The washing down of chalk from an excessively eroding paint onto another area below (a brick foundation, for example), ruining its appearance (see Chalking).
POSSIBLE CAUSES:
Use of a lower quality, highly pigmented paint.
Use of an interior paint for an outdoor application.
Over dilution of masonry coating
SOLUTION:
Remove as much of the chalk residue as possible (see Chalking) using a stiff bristle brush, then apply Sandtex Trade Stabilising Solution.
If the affected area dries to a different colour, consider re-painting.