Ferroflex 423 is a crystallizing and flexible cementitious waterproofing material. It contains cement, mineral powder, and special chemicals that react with calcium hydroxide to form crystals within the concrete's pores.

This continuous crystallization provides long-term protection against water leakage. The material also has slight flexibility, allowing it to effectively seal small hairline cracks in the concrete surface. This makes it particularly effective at withstanding both positive and negative water pressure.