Concrete additives that allow the pores and capillaries of the mixture to close. Water can penetrate the concrete either by pressure (deposits, pipes, etc.), or by capillarity (contact with a wet environment). When a water-repellent concrete has been correctly dosed, made and placed, it is generally impermeable in itself, the more the smaller its capillary network, that is, the greater its compactness.
The capillary network is formed by the evaporation of excess kneading water over the strictly necessary to hydrate the cement. This excess is always necessary to be able to handle and place the concrete, and it should be, as obvious, as small as possible. The hair network will be all the more important when:
less finely ground is the cement
higher the water / cement ratio
worse the granulometric composition of concrete
the shorter the cure
In view of the above, mass waterproofing agents can be used which, by closing the pores and capillaries, improve the compactness of the assembly. But it is evident that its effect will be null if such pores or capillaries are not relatively small, that is, if the concrete or concrete is poorly dosed or executed. In short, you cannot waterproof a concrete