Waterproof or water-resistant describes objects unaffected by water or resisting water passage, or which are covered with a material that resists or does not allow water passage. Such items may be used in wet environments or under water. Waterproofing describes making an object waterproof or water-resistant.

The hulls of boats and ships were once waterproofed by applying tar or pitch. Modern items may be waterproofed by applying water-repellent coatings or by sealing seams with gaskets or O-rings.

In construction, a building or structure is waterproofed with the use of membranes to protect contents underneath or within as well as protecting structural integrity. The waterproofing of the building envelope in construction specifications is under '07 - Thermal and Moisture' protection and includes roofing material as well as waterproofing materials.

Waterproofing is used in reference to building structures (basements, decks, flat roofs, wet areas, etc.), watercraft, canvas, clothing and paper (e.g., milk and juice cartons).

Construction Waterproofing

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 systemsas 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 include Hydrotech's 1 Monolithic Membrane 6125 (MM6125) and Re-New's 2 Turbo Seal. These new 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.