We Supply Waterproofing Cement Sika. MasterSeal 501 is used as a capillary waterproofing system for concrete and masonry structures to provide permanent, integral waterproofing against water leakage and chemical attack. It is applied as a slurry or used as a dry shake on surfaces like water tanks, reservoirs, basements, swimming pools, and sewage treatment plants. The product works by forming insoluble crystals within the concrete's pores and capillaries, which block water passage and can be reactivated by subsequent water contact.