ABSTRACT

A wide range of surface coatings are available and can be chosen to provide progressively increasing protection. All coatings should at least provide resistance to water in its liquid state, while more impermeable coatings also resist the ingress of carbon dioxide and the most impermeable coatings additionally provide a barrier to water vapour. It is generally assumed that chloride ions can only be transported into concrete, or diffuse through concrete, in liquid phase water. A hydrophobic coating such as a silane will therefore generally hinder the ingress of chlorides but may still allow the concrete to carbonate. It has been argued that this type of coating, by keeping the concrete in a less saturated condition, will allow it to carbonate faster. However, corrosion is less likely in the drier concrete. Water vapour permeance (breathability) is generally considered to be a desirable quality in a coating as it allows moisture in the concrete to escape. Complete impermeability to water vapour can lead to failure of the coating due to loss of adhesion if water vapour pressures can build up behind the coating.