Water repellency is another important property for a coating to be
able to correctly protect the support against water penetration.
Surface modyfing agents help to improve the water resistance by lowering the surface
tension so that the wetting of the paint film becomes harder. The hydrophobic characteristic
of the coating film is enhanced.
Figure 1: Improvement of water repellency
Two main additives categories can help to increase this property:
Silicones especially bring to coatings a very high water repellency resulting
in low water absorption. This resistance to water is particularly useful since it
is relatively unaffected by temperature and climatic variations.
Waxes perform also very well, particularly on porous surfaces. The oil penetrates
easily within the pores and fissures, rapidly imparting a very hydrophobic character
to the treated surface.