Chalking

Decomposition of the binding agents at the paint surface resulting in the release of the colour pigments. Reds and yellow colours turn whitish and dark blues turn bronze.

Formation of fine powder on the surface of the paint film during weathering which can cause color fading. Although some degree of chalking is a normal, desirable way for a paint film to wear, excessive film erosion can result from heavy chalking.

Paint defects
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Chalk
Chalk
Chalk

Cause

  • Choice of wrong hardener or amount.
  • Colour coats applied to thick.
  • Weathering (aggressive environmental pollution such as sulphur dioxide and nitrous oxides in combination with high
    humidity and exposure to UV radiation).
  • Over thinning the paint.
  • Poor repair to a previously chalking paint
    finish.

Prevention

  • Always use  recommended hardener and mixing ratio.
  • Always keep to the recommended film thickness and number of coats. For colours with poor covering power (yelllow’s reds etc), use a coloured surfacer (as used by OEM Automotive Industry).
  • Avoid exposure to ultraviolet light (strong sunlight) and harsh shampoos.
  • Ensure chalked paintwork is removed back to a sound substrate before refinishing.
  • Use base coat + clear lacquer system where possible.

Remedy

  • Try to polish out the problem using a fine
    polishing paste and finish with a high gloss polish.
  • If the chalked surfaces do not respond to this action, or if the problem returns within a short period (a few weeks), then the damaged paintwork must be removed back to a sound substrate and refinished.
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