Whiteness, opacity, reduces porosity.
Berger WeatherCoat Exterior Primer is formulated with special grade pigment, that provides extra whiteness with excellent opacity. It is water base primer for exterior walls and a suitable undercoat for exterior emulsions. It gives a tough film and as a result is helps to provide longer life of total paint system. No curing is required for this primer. It penetrates the porous surface, seals the porosity of the surface, reduces the absorption of the surface and as a result top coat gives better coverage.
For exteriors, it is wise to go for undercoats with transparent films as they prevent the penetration of water into the walls