The economical way to protect it from ingress of rainwater, polymer and cement is mixed together to achieve paintable slurry which seals the porosity of the surface and acts as a waterproof barrier. Two to three coats are applied with brush on leaky surfaces which act as a waterproof paint.
Elastomeric Cementitious waterproof slurry is another improved system for underlayment treatment for treating leaky concrete surfaces. It is then covered by layer of mortar to protect it by wear & tear.
Acrylic based flexible single component terrace waterproof coatings are also available from various manufacturers. These coatings although more expensive have a better life span of about 3-4 years depending on the condition of the building structure.