SikaTop-501 Seal (formerly known as MasterSeal 501) is a premium, cement-based capillary crystalline waterproofing material. It is applied directly to concrete and blockwork structures to provide a permanent barrier against water leakage, ingress, or seepage. The chemical active ingredients react with moisture inside the concrete to grow insoluble crystals within the capillary pores, effectively sealing the pathways for water.