Generally, water based protective coatings are more permeable to gases and water vapour. These coatings are formulated by using polymer dispersions. Water vapour permeability is a desirable property to allow water vapour to escape from the substrate. But, if the permeability is too high, carbon dioxide can diffuse from atmosphere into the substrate easily. Hence there is a need for coatings with moderate gas permeability which can prevent Carbon dioxide from diffusing into the substrate while allowing moisture to escape.
Carbonation is a natural process and is virtually impossible to avoid unprotected concrete as the process begins as soon as concrete is exposed to the elements. Carbon dioxide from the atmosphere reacts with the concrete, leading to a loss of alkalinity and subsequent corrosion of the reinforcing steel.
Protective coatings are formulated to prevent the diffusion of Carbon dioxide and thereby protect concrete structures from the detrimental effects, carbonation.