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Chalking is identified by the fine chalky powder that forms on the surface of a paint film. Although some chalking is a normal way in which paints self-clean when exposed to the sun and rain, excessive chalking can indicate paint failure. In dry arid climates where there is little rain, chalking can become excessive. Chalking is actually the paint pigment released by the paint binders that have been broken down by exposure to the weather. Chalking is especially common with very light-coloured flat paints, especially lesser quality oil-based paints containing high levels of pigment extenders. When chalking gets severe, it may run off and stain the surrounding construction.

Possible Causes

o Cheaper-quality exterior paint was used, containing high levels of pigment extenders.
o Improper paint (such as interior paint) was used in an exterior application.
o Paint was applied over lower-quality factory-finished aluminium siding.
o The paint was over-thinned before it was applied.
o Porous surfaces were not properly sealed before painting.

Repair and Prevention

o Chalking must be removed before repainting. Remove chalking by power washing or scrubbing with a trisodium phosphate cleaning solution and rinse with clean water. Let dry and paint with a high-quality latex house paint.
o To clean brick areas stained by chalking runoff, the masonry should be scrubbed with a specialised masonry cleaning solution. If staining persists, a professional cleaning contractor may be required to clean the brick.

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