Degradation, durability of paints

he purpose of this dossier is to present the main types of deterioration in paint coatings applied to substrates commonly encountered in building and civil engineering: masonry and exterior coatings, wood and wood materials, and the main metal construction materials. It covers the deterioration and defects that occur in coatings after a few years' exposure. In most cases, it gives indications of possible causes of deterioration.

However, it is not the purpose of this dossier to describe initial problems and pathologies that appear during paint application or in the hours that follow. In fact, anomalies of this type are dealt with in the "Protection and decoration by paint" file. . It should be noted that such anomalies can generally be dealt with by personnel qualified in the use of application equipment (e.g. certified operators) or, in the case of product preparation precautions, substrate condition or atmospheric conditions, by a suitably qualified operator (see § 1.4.2 Certification of paint systems and operators).

Nor is it the purpose of this dossier to establish the precise causes of the various paint coating degradations. Indeed, for each case, establishing the precise causes requires the expertise of competent controllers or inspectors, who will be informed of the details of the problem. In fact, degradations that appear to be equivalent, or even similar, may have their origins in quite different phenomena.

Why adopt a plan based on the main types of material used to support the paint coating?

The reason is quite simple. A coating of this kind generally has a thickness of less than one millimetre. Moreover, one of its main qualities is to be sufficiently adherent to its substrate (the substrate of the coating is preferably referred to as the "substrate"). It is therefore virtually automatic that defects in the substrate will be transmitted to the coating.

This is often the case for deformations in the substrate, such as cracks and living microcracks, which change width according to movement:

• of thermal origin between hot and cold periods (case of masonry and concrete);

• or due to variations in moisture content...