Add one bag of RS-500 (2kg) into the mixture of cement and sand. The amount of cement and sand should be 50kg and 150kg respectively. In general the ratio of cement and sand should be 1:3.
RS-500 originates from inorganic soil found in Sea of Japan and German engineering. It is designed to provide excellent waterproofing and minor crack auto-sealing for concrete mixture. Due to its effectiveness on negative-side waterproof and moisture proof RS-500 can also be applied to prevent efflorescence.