What causes exterior paint to chalk?
The formation of chalk (fine, white powder) on the surface of a painted surface is primarily due to weathering, which can give the appearance of color fading. While some degree of chalking is normal and can be a desirable way for paint to wear, excessive paint film erosion may result in heavy chalking.
THERE ARE SEVERAL POSSIBLE CAUSES
1. Oil-based paints have a tendency to chalk more than do latex paints.
2. Use of a low-grade paint, or a highly pigmented paint.
3. Factory-finished siding often develops an thick chalk layer and generally requires power washing to ensure complete chalk removal.
4. Not properly sealing a porous surface.
5. Over-thinning or watering down the paint.
6. Spreading the paint too thin.
7. Using interior paint in an outdoor location.
Some degree of chalking is normal. Some paint manufacturers have even touted this as a “self-cleaning” process. However, excessive film erosion can result in unsightly heavy chalk. Excessive chalking is caused by the disintegration of the paint film during weathering. Some common causes of heavy chalking include application to an unsealed surface, overspreading the paint, or poor quality paint. All can lead to premature breakdown by the weather.
