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Chalking is the progressive powdering of the paint film on the painted surface.

The primary reason for the problem is polymer degradation of the paint matrix due to exposure of UV radiation in sunshine and condensation from dew.

The degree of chalking varies as epoxies react quickly while acrylics and polyurethanes can remain unchanged for long periods.

The degree of chalking can be assessed according to International Standard ISO 4628 Part 6 or 7 or American Society of Testing and Materials ( ASTM ) Method D4214 ( Standard Test Methods for Evaluating the Degree of Chalking of Exterior Paint Films ).