Definition: The formation of fine powder on the surface of the paint, due to weathering.
Progression: All paints chalk to some degree; it is a normal, desirable way for the paint film to wear. Quality paints may chalk mildly, but still maintain a sound surface for many years. Medium and heavy chalking can cause color fading. Severe chalking makes repainting a problem because it does not provide a good surface to which new paint can adhere.
* Long-term exposure to moisture and sunlight
* Using a low-quality paint can be a problem and cause chalking
* Over thinning the paint or spreading it too thin
* Not priming and sealing a porous surface
* Determine the degree of chalking by rubbing the surface with a finger or dark cloth.
* Remove all chalk residue by one of these methods:
- Excessive chalking requires pressure-washing or sand-blasting. If a pressure washer is not available, scrub the surface with a stiff brush and a mild detergent. Rinse thoroughly with a strong stream of water from a garden hose.
- Light to moderately chalked surfaces may require wire-brushing or sanding to remove the excess surface powder. Spray the surface with a strong stream from a garden hose.
- Allow the surface to dry thoroughly.
- Problem Chalking
* Check the surface again using your finger or a rag to determine the amount of chalk residue.
- If little or no chalk remains and the old paint is in good condition, no priming is necessary.
- If light to moderate chalk remains, use a penetrating additive to the first coat of water-based paint to help the paint film bond to the chalked surface. 100% acrylic finishes provide better chalk resistance than vinyl-acrylic paints.
- Problem Chalking
* If noticeable chalk still remains, use an alkyd-based masonry primer as the first coat of paint. Finish using a high-quality topcoat.
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