Chalking Paint

Definition

Chalking refers to the formation of a white, powdery residue on painted surfaces as the paint begins to break down, particularly in exterior settings where it's exposed to the elements. 

Basic Information

Chalking is a natural process that occurs as certain types of paint weather and degrade over time. It is especially common in exterior paints that have been exposed to UV radiation, moisture, or temperature extremes. The breakdown of the paint's binder releases pigment particles, resulting in the chalky residue. While it doesn't always affect the protective properties of the paint, chalking can cause fading, an unattractive appearance, and issues with repainting if left untreated.

This issue is often seen on older painted surfaces, particularly exterior walls, fences, or trim, but it can also occur indoors in areas exposed to high humidity.

Common Causes

• Weathering: Prolonged exposure to sun, wind, and rain can cause the paint's binder to break down, releasing pigment as a powder.

• Low-Quality Paint: Paints with a low resin content or those not designed for outdoor use are more prone to chalking, as they break down more quickly under harsh conditions.

• Over-thinning: Thinning paint is generally never recommended, and in regards to chalking, it can weaken the binder, accelerating the deterioration.

Progression

Chalking starts with small patches of powdery residue and gradually spreads across the surface. If not addressed, it can lead to further degradation of the paint and the underlying surfaces. Chalking can sometimes be more noticeable on darker colours. Over time, the chalky residue may run down the surface during rain, creating streaks or stains. Additionally, if chalking is excessive, it can make future painting jobs more difficult, as the loose powder needs to be cleaned properly before the surface will be ready to be repainted.

Solution

• Use High-Quality Exterior Paint: Opt for paints specifically formulated for outdoor use, with strong binders and resistance to weathering.

• Proper Surface Preparation: Before repainting, clean the surface thoroughly to remove chalking residue. A pressure wash or scrubbing with a neutral cleaning agent and water can help ensure a clean surface for better adhesion.

• Avoid Thinning or Over-Thinning: Follow manufacturer guidelines for thinning paint to ensure that it maintains the proper consistency and binder strength.

• Repaint When Necessary: When chalking becomes severe, repainting is often the best solution. Be sure to clean/prepare/prime the surface using the appropriate materials for the paint you are going to be using.

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