Exterior paint is constantly exposed to sunlight, rain, and dust. Over time, a fine white powder often appears on the wall surface. This phenomenon is known as the chalking defect, a common issue in paint application and maintenance. It not only reduces aesthetic value but also affects the durability and protective ability of the coating. Understanding the causes and mechanism of chalking helps maintain long-lasting color stability for exterior surfaces.
WHAT IS CHALKING IN PAINT
Chalking is the process in which the paint film ages and forms a fine white powder on its surface. When touched, the surface leaves a white residue like dust or chalk. The main reason is the breakdown of polymer bonds within the paint film, causing pigments and additives to separate from the binder. Chalking often occurs on walls exposed to intense sunlight or heavy rainfall. In mild cases, it only dulls the surface; in severe cases, it can lead to fading, flaking, and loss of adhesion.
CAUSES OF EXTERIOR PAINT FADING AND CHALKING
The impact of UV rays and weather
Ultraviolet (UV) radiation in sunlight is the main factor that damages the paint film. Under UV exposure, the polymer chains in the binder are broken, weakening the paint’s structure. As the binder deteriorates, pigments become unprotected and detach, forming a chalky layer. Rain, wind, high temperatures, and humidity fluctuations further speed up this process. Walls facing west or south, which receive the most sunlight, usually fade faster than shaded areas.
Paint quality and unstable composition
The composition of paint directly affects its resistance to chalking. Low-quality binders or paints with insufficient resin content are more prone to degradation. Cheap paints often use organic pigments that lack lightfastness and deteriorate easily under sunlight. If the paint formula lacks antioxidants and UV stabilizers, chalking can appear after just a few months. Therefore, choosing a paint with stable, tested ingredients is essential for long-term protection.
Errors during application
Many premature chalking problems result from improper painting procedures. When the wall surface is still damp or has a high pH, chemical reactions between paint and substrate destroy polymer bonds. Skipping the primer or using an incompatible one also weakens adhesion. Applying paint in harsh conditions such as direct sunlight, high humidity, or strong wind prevents even film formation. Inadequate film thickness or insufficient coats also accelerate paint degradation.
EFFECTS OF CHALKING ON SURFACE AND COATING DURABILITY
Chalking causes color fading, loss of gloss, and uneven surface appearance. The white powder layer scatters light poorly, making the wall look dull and aged. It also reduces the adhesion of new coats during repainting. If left untreated, the paint film can peel, crack, and allow water penetration. Moisture encourages the growth of mold and algae, further damaging the surface. Over time, chalking increases maintenance costs and significantly shortens the lifespan of the painted surface.
SOLUTIONS TO CONTROL AND PREVENT CHALKING DEFECTS
For surfaces already affected by chalking
First, thoroughly clean the chalky residue with a soft brush, damp cloth, or high-pressure washer. Allow the surface to dry naturally for at least 24 hours. Then, apply a high-quality alkali-resistant primer that penetrates deeply and enhances adhesion. Finish with one or two coats of premium exterior paint containing UV absorbers and antioxidants. Acrylic or polyurethane-based paints are ideal thanks to their color retention and excellent weather resistance.
For newly painted surfaces
Always check wall moisture (below 16%) and pH (below 9) before painting. Use a three-layer paint system consisting of primer, intermediate, and topcoat. Apply in dry weather, at temperatures between 25–35°C, to ensure proper film formation. Choose paints formulated for outdoor use with built-in UV stabilizers to resist fading and degradation.
VICHEM – OFFICIAL DISTRIBUTOR OF CHEMICAL ADDITIVES FROM COVESTRO, SINOPEC, AND TINOX IN VIETNAM
Vichem is the authorized distributor of chemical additives from major global brands such as Covestro, Sinopec, Tinox, and TotalEnergies in Vietnam, fully compliant with local legal regulations. We not only provide high-quality products but also deliver international-standard after-sales services. Our services include:
- Technical consulting: Assisting customers in selecting the most suitable products for their specific applications.
- Color matching tests: Vichem’s technical team performs color-matching trials to ensure results meet design and performance standards.
- Application support: Working closely with customers during process integration to guarantee optimal performance and stable quality.
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