Last edited 14 Dec 2020



Waterproofing is a process that ensures a structure or object is able to keep out 100% of any water that comes into contact with it. In construction, waterproofing can increase the life of common materials like concrete, iron, paint and more. Although it is not common to refer to a building as being 'waterproof' (although it would not be wrong and would be understood by most), it is more common to use the term ‘watertight’ or 'weatherproof'.

A new building will reach a stage in construction where it is made watertight to prevent water from penetrating into internal areas. Alternatively, an existing building may undergo remedial works to make its basement watertight, to prevent penetrating damp or rising damp and so on. For more information see: Damp proofing.

However, the term waterproof can be applied to particular elements of the building fabric that are designed to keep out water. For example, although high-grade concrete can be highly impervious to moisture this is difficult to achieve in practice due to a number of construction reasons. But when PVC or copper water bars are incorporated at joints (the weak points) and a waterproofing agent is added to the mix, a waterproof construction can be achieved.

Similarly, a synthetic roofing membrane may be termed waterproof not only because water is unable to penetrate the molecular structure of the material but also because it can form a continuous, seamless roof surface that can be waterproof when properly installed.

In contrast, a slate roof may be termed watertight as it will generally do an excellent job of keeping water out. However, in severe weather conditions (such as wind driven rain) it may not be waterproof since water ingress may occur through joints. Cladding systems such as rainscreen cladding may allow water to penetrate through a first layer of defence, but this is then drained away before reaching the interior.

Cementitious waterproofing is a method of waterproofing used in wet areas like toilets and bathrooms. This is a semi-flexible or rigid type of waterproofing, and material should not be exposed to weathering or sunlight.

More flexible than cementitious waterproofing, liquid membrane waterproofing is a thin coating of primer and two top coats.The liquid cures into a rubbery coating on surfaces and can provide high elongation. The durability of the coating depends on what type of polymer is used.

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