Leak Sealing is the term used for stopping water ingress into a structure. This can be minor but the resins can be used to stop gushing water. These products are expanding Polyurethane grouts that are injected into live cracks under pressure. Once in contact with water they expand up to 30 times their original volume, thus cutting off the flow of water. Acrylic gels can also be pumped in to create a more permanent membrane.