PU is a hydrophobic polyurethane grout designed to stop water leaks. It is typically injected into cracks in concrete, honeycombed concrete, soils, pipes, pipe intrusions and other voids by use of a high pressure pump. When the liquid polyurethane meets water or moisture it reacts with it and then expands, creating a dense, closed cell foam through which water will not pass. In an unconfined environment the expansion rate of the material is 20 times its own volume.
PU is typically used to stop water leaks coming through cracked or honey-combed concrete voids between wall and floor, wall and ceiling, expansion joints, cold joints and pipe intrusions. It is used to repair concrete walls, ceilings and floors that are leaking; in tunnels, including limestone, manholes, sewer lines and in concrete dams.
A building or structure needs waterproofing as concrete itself will not be watertight on its own. The conventional system of waterproofing involves 'membranes'. This relies on the application of one or more layers of membrane (available in various materials: e.g., bitumen, silicate, PVC, HDPE, etc.) that act as a barrier between the water and the building structure, preventing the passage of water. However, the membrane system relies on exacting application, presenting difficulties. Problems with application or adherence to the substrate can lead to leakage.
Over the past two decades, the construction industry has had technological advances in waterproofing materials, including integral waterproofing systems as well as more advanced membrane materials.
Integral systems work within the matrix of a concrete structure, giving the concrete itself a waterproof quality. There are two main types of integral waterproofing systems: the hydrophilic and the hydrophobic systems. A hydrophilic system typically uses a crystallization technology that replaces the water in the concrete with insoluble crystals. Various brands available in the market claim similar properties, but not all can react with a wide range of cement hydration by-products, and thus require caution. Hydrophobic systems use fatty acids to block pores within the concrete, preventing water passage.
New membrane materials seek to overcome shortcomings in older methods like PVC and HDPE. Generally, new technology in waterproof membranes relies on polymer based materials that are extremely adhesive to create a seamless barrier around the outside of a structure.