What is chalking?
Chalking is the appearance of a loosely adherent fine powder on the surface of a paint film arising from the degradation of one or more of its constituents.
If the coating itself is breaking down due to ultraviolet (UV) degradation, there will be some evidence of a white or coloured powdery “chalking” residue on the wipe-cloth. Some chalking is to be expected as all paints will be affected by UV radiation to some degree, over time.
The rate of this degradation will vary depending on the topcoat colour, environmental conditions and the type of paint used (ie. the particular resin system used in a given paint product).
The Dulux® Weathershield® guarantee covers premature blistering, flaking and peeling of the coating system however it does not cover fading (colour change) or “chalking” of the paint film. This is because there are factors outside of the manufacturer’s control – such as prevailing climate and weather conditions – that can strongly influence the performance of a paint film.
Why does chalking occur?
Chalking occurs due to ultraviolet (UV) radiation from sunlight interacting with the constituents within the paint film. Overtime UV degradation of the binder or resin within the paint film will allow the exposed pigment particles to become more loosely bound to the surface. A powdery surface is the result.
Chalking is a natural process that happens slowly over time. Chalking may also result in colour fading or poor colour retention. Some chalking/fading is expected as the paint film weathers and an acceptable level of deterioration is set-out under various sub-sections of AS 3730 (2006) Latex-Exterior- coatings.
The following factors, beyond the control of the manufacturer or applicator, are known to accelerate such behaviour in paints:
- Sunlight and ultraviolet (UV) radiation
- Hot/cold temperature cycling
- Application of darker coloured paint
- Coastal environments
- Correct film thickness
- Wrong product
The solution for chalking
Unfortunately, degradation due to the “chalking” is irreversible once it begins to occur and the appearance can often become quite irregular or patchy in appearance.
To eliminate the effect completely, the entire surface will need to be pressure washed and/or scrubbed with a non-metallic scouring pad to remove all surface contaminants and chalking prior to repainting with an approved UV resistant coating system*.
Prevention of chalking
The use of a water-based 100% acrylic latex topcoat will provide superior exterior durability and gloss retention relative to many alternative coatings systems, especially oil based enamels.
This information has been sourced from Dulux Technical Advice on Chalking.